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Merge pull request #3189 from visr/julia1
[julia/en] update to run on julia 1.0
This commit is contained in:
Adam Bard
GitHub
commit
ba713d7261
@ -2,17 +2,17 @@
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language: Julia
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contributors:
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- ["Leah Hanson", "http://leahhanson.us"]
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- ["Pranit Bauva", "http://github.com/pranitbauva1997"]
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- ["Daniel YC Lin", "http://github.com/dlintw"]
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- ["Pranit Bauva", "https://github.com/pranitbauva1997"]
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- ["Daniel YC Lin", "https://github.com/dlintw"]
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filename: learnjulia.jl
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---
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Julia is a new homoiconic functional language focused on technical computing.
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While having the full power of homoiconic macros, first-class functions, and low-level control, Julia is as easy to learn and use as Python.
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This is based on Julia 0.6.4
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This is based on Julia 1.0.0
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```ruby
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```julia
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# Single line comments start with a hash (pound) symbol.
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#= Multiline comments can be written
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@ -27,38 +27,38 @@ This is based on Julia 0.6.4
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# Everything in Julia is an expression.
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# There are several basic types of numbers.
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3 # => 3 (Int64)
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3.2 # => 3.2 (Float64)
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2 + 1im # => 2 + 1im (Complex{Int64})
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2//3 # => 2//3 (Rational{Int64})
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3 # => 3 (Int64)
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3.2 # => 3.2 (Float64)
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2 + 1im # => 2 + 1im (Complex{Int64})
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2 // 3 # => 2 // 3 (Rational{Int64})
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# All of the normal infix operators are available.
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1 + 1 # => 2
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8 - 1 # => 7
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10 * 2 # => 20
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35 / 5 # => 7.0
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5 / 2 # => 2.5 # dividing an Int by an Int always results in a Float
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div(5, 2) # => 2 # for a truncated result, use div
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5 \ 35 # => 7.0
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2 ^ 2 # => 4 # power, not bitwise xor
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12 % 10 # => 2
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1 + 1 # => 2
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8 - 1 # => 7
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10 * 2 # => 20
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35 / 5 # => 7.0
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5 / 2 # => 2.5 # dividing integers always results in a Float64
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div(5, 2) # => 2 # for a truncated result, use div
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5 \ 35 # => 7.0
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2^2 # => 4 # power, not bitwise xor
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12 % 10 # => 2
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# Enforce precedence with parentheses
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(1 + 3) * 2 # => 8
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(1 + 3) * 2 # => 8
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# Bitwise Operators
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~2 # => -3 # bitwise not
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3 & 5 # => 1 # bitwise and
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2 | 4 # => 6 # bitwise or
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xor(2, 4) # => 6 # bitwise xor
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2 >>> 1 # => 1 # logical shift right
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2 >> 1 # => 1 # arithmetic shift right
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2 << 1 # => 4 # logical/arithmetic shift left
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~2 # => -3 # bitwise not
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3 & 5 # => 1 # bitwise and
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2 | 4 # => 6 # bitwise or
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xor(2, 4) # => 6 # bitwise xor
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2 >>> 1 # => 1 # logical shift right
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2 >> 1 # => 1 # arithmetic shift right
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2 << 1 # => 4 # logical/arithmetic shift left
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# You can use the bits function to see the binary representation of a number.
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bits(12345)
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# Use the bitstring function to see the binary representation of a number.
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bitstring(12345)
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# => "0000000000000000000000000000000000000000000000000011000000111001"
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bits(12345.0)
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bitstring(12345.0)
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# => "0100000011001000000111001000000000000000000000000000000000000000"
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# Boolean values are primitives
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@ -66,48 +66,38 @@ true
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false
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# Boolean operators
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!true # => false
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!false # => true
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1 == 1 # => true
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2 == 1 # => false
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1 != 1 # => false
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2 != 1 # => true
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1 < 10 # => true
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1 > 10 # => false
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2 <= 2 # => true
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2 >= 2 # => true
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!true # => false
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!false # => true
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1 == 1 # => true
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2 == 1 # => false
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1 != 1 # => false
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2 != 1 # => true
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1 < 10 # => true
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1 > 10 # => false
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2 <= 2 # => true
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2 >= 2 # => true
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# Comparisons can be chained
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1 < 2 < 3 # => true
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2 < 3 < 2 # => false
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1 < 2 < 3 # => true
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2 < 3 < 2 # => false
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# Strings are created with "
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try
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"This is a string."
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catch ; end
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# Julia has several types of strings, including ASCIIString and UTF8String.
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# More on this in the Types section.
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# Character literals are written with '
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try
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'a'
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catch ; end
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# Some strings can be indexed like an array of characters
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try
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"This is a string"[1] # => 'T' # Julia indexes from 1
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catch ; end
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# However, this is will not work well for UTF8 strings,
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# so iterating over strings is recommended (map, for loops, etc).
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# Strings are UTF8 encoded. Only if they contain only ASCII characters can
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# they be safely indexed.
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ascii("This is a string")[1] # => 'T' # Julia indexes from 1
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# Otherwise, iterating over strings is recommended (map, for loops, etc).
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# $ can be used for string interpolation:
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try
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"2 + 2 = $(2 + 2)" # => "2 + 2 = 4"
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catch ; end
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# You can put any Julia expression inside the parentheses.
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# Another way to format strings is the printf macro.
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@printf "%d is less than %f" 4.5 5.3 # 4 is less than 5.300000
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# Another way to format strings is the printf macro from the stdlib Printf.
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using Printf
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@printf "%d is less than %f\n" 4.5 5.3 # => 5 is less than 5.300000
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# Printing is easy
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println("I'm Julia. Nice to meet you!")
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@ -115,29 +105,29 @@ println("I'm Julia. Nice to meet you!")
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# String can be compared lexicographically
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"good" > "bye" # => true
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"good" == "good" # => true
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"1 + 2 = 3" == "1 + 2 = $(1+2)" # => true
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"1 + 2 = 3" == "1 + 2 = $(1 + 2)" # => true
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####################################################
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## 2. Variables and Collections
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####################################################
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# You don't declare variables before assigning to them.
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some_var = 5 # => 5
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some_var # => 5
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some_var = 5 # => 5
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some_var # => 5
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# Accessing a previously unassigned variable is an error
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try
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some_other_var # => ERROR: some_other_var not defined
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some_other_var # => ERROR: UndefVarError: some_other_var not defined
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catch e
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println(e)
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end
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# Variable names start with a letter or underscore.
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# After that, you can use letters, digits, underscores, and exclamation points.
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SomeOtherVar123! = 6 # => 6
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SomeOtherVar123! = 6 # => 6
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# You can also use certain unicode characters
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☃ = 8 # => 8
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☃ = 8 # => 8
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# These are especially handy for mathematical notation
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2 * π # => 6.283185307179586
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@ -156,165 +146,168 @@ SomeOtherVar123! = 6 # => 6
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# functions are sometimes called mutating functions or in-place functions.
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|
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# Arrays store a sequence of values indexed by integers 1 through n:
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a = Int64[] # => 0-element Int64 Array
|
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a = Int64[] # => 0-element Int64 Array
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|
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# 1-dimensional array literals can be written with comma-separated values.
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b = [4, 5, 6] # => 3-element Int64 Array: [4, 5, 6]
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b = [4; 5; 6] # => 3-element Int64 Array: [4, 5, 6]
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b[1] # => 4
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b[end] # => 6
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b = [4, 5, 6] # => 3-element Int64 Array: [4, 5, 6]
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b = [4; 5; 6] # => 3-element Int64 Array: [4, 5, 6]
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b[1] # => 4
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b[end] # => 6
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# 2-dimensional arrays use space-separated values and semicolon-separated rows.
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matrix = [1 2; 3 4] # => 2x2 Int64 Array: [1 2; 3 4]
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matrix = [1 2; 3 4] # => 2x2 Int64 Array: [1 2; 3 4]
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# Arrays of a particular Type
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b = Int8[4, 5, 6] # => 3-element Int8 Array: [4, 5, 6]
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# Arrays of a particular type
|
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b = Int8[4, 5, 6] # => 3-element Int8 Array: [4, 5, 6]
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# Add stuff to the end of a list with push! and append!
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push!(a,1) # => [1]
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push!(a,2) # => [1,2]
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push!(a,4) # => [1,2,4]
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push!(a,3) # => [1,2,4,3]
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append!(a,b) # => [1,2,4,3,4,5,6]
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push!(a, 1) # => [1]
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push!(a, 2) # => [1,2]
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push!(a, 4) # => [1,2,4]
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push!(a, 3) # => [1,2,4,3]
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append!(a, b) # => [1,2,4,3,4,5,6]
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# Remove from the end with pop
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pop!(b) # => 6 and b is now [4,5]
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pop!(b) # => 6 and b is now [4,5]
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# Let's put it back
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push!(b,6) # b is now [4,5,6] again.
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push!(b, 6) # b is now [4,5,6] again.
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a[1] # => 1 # remember that Julia indexes from 1, not 0!
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a[1] # => 1 # remember that Julia indexes from 1, not 0!
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# end is a shorthand for the last index. It can be used in any
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# indexing expression
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a[end] # => 6
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a[end] # => 6
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# we also have shift and unshift
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shift!(a) # => 1 and a is now [2,4,3,4,5,6]
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unshift!(a,7) # => [7,2,4,3,4,5,6]
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# we also have popfirst! and pushfirst!
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popfirst!(a) # => 1 and a is now [2,4,3,4,5,6]
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pushfirst!(a, 7) # => [7,2,4,3,4,5,6]
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# Function names that end in exclamations points indicate that they modify
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# their argument.
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arr = [5,4,6] # => 3-element Int64 Array: [5,4,6]
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sort(arr) # => [4,5,6]; arr is still [5,4,6]
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sort!(arr) # => [4,5,6]; arr is now [4,5,6]
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arr = [5,4,6] # => 3-element Int64 Array: [5,4,6]
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sort(arr) # => [4,5,6]; arr is still [5,4,6]
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sort!(arr) # => [4,5,6]; arr is now [4,5,6]
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# Looking out of bounds is a BoundsError
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try
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a[0] # => ERROR: BoundsError() in getindex at array.jl:270
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a[end+1] # => ERROR: BoundsError() in getindex at array.jl:270
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a[0]
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# => BoundsError: attempt to access 7-element Array{Int64,1} at index [0]
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a[end + 1]
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# => BoundsError: attempt to access 7-element Array{Int64,1} at index [8]
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catch e
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println(e)
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end
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# Errors list the line and file they came from, even if it's in the standard
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# library. If you built Julia from source, you can look in the folder base
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# inside the julia folder to find these files.
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# library. You can look in the folder share/julia inside the julia folder to
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# find these files.
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# You can initialize arrays from ranges
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a = [1:5;] # => 5-element Int64 Array: [1,2,3,4,5]
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a = [1:5;] # => 5-element Int64 Array: [1,2,3,4,5]
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|
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# You can look at ranges with slice syntax.
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a[1:3] # => [1, 2, 3]
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a[2:end] # => [2, 3, 4, 5]
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a[1:3] # => [1, 2, 3]
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a[2:end] # => [2, 3, 4, 5]
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|
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# Remove elements from an array by index with splice!
|
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arr = [3,4,5]
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splice!(arr,2) # => 4 ; arr is now [3,5]
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splice!(arr, 2) # => 4 ; arr is now [3,5]
|
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|
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# Concatenate lists with append!
|
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b = [1,2,3]
|
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append!(a,b) # Now a is [1, 2, 3, 4, 5, 1, 2, 3]
|
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append!(a, b) # Now a is [1, 2, 3, 4, 5, 1, 2, 3]
|
||||
|
||||
# Check for existence in a list with in
|
||||
in(1, a) # => true
|
||||
in(1, a) # => true
|
||||
|
||||
# Examine the length with length
|
||||
length(a) # => 8
|
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length(a) # => 8
|
||||
|
||||
# Tuples are immutable.
|
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tup = (1, 2, 3) # => (1,2,3) # an (Int64,Int64,Int64) tuple.
|
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tup[1] # => 1
|
||||
try:
|
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tup[1] = 3 # => ERROR: no method setindex!((Int64,Int64,Int64),Int64,Int64)
|
||||
tup = (1, 2, 3) # => (1,2,3) # an (Int64,Int64,Int64) tuple.
|
||||
tup[1] # => 1
|
||||
try
|
||||
tup[1] = 3 # => ERROR: no method setindex!((Int64,Int64,Int64),Int64,Int64)
|
||||
catch e
|
||||
println(e)
|
||||
end
|
||||
|
||||
# Many list functions also work on tuples
|
||||
length(tup) # => 3
|
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tup[1:2] # => (1,2)
|
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in(2, tup) # => true
|
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# Many array functions also work on tuples
|
||||
length(tup) # => 3
|
||||
tup[1:2] # => (1,2)
|
||||
in(2, tup) # => true
|
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|
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# You can unpack tuples into variables
|
||||
a, b, c = (1, 2, 3) # => (1,2,3) # a is now 1, b is now 2 and c is now 3
|
||||
a, b, c = (1, 2, 3) # => (1,2,3) # a is now 1, b is now 2 and c is now 3
|
||||
|
||||
# Tuples are created even if you leave out the parentheses
|
||||
d, e, f = 4, 5, 6 # => (4,5,6)
|
||||
d, e, f = 4, 5, 6 # => (4,5,6)
|
||||
|
||||
# A 1-element tuple is distinct from the value it contains
|
||||
(1,) == 1 # => false
|
||||
(1) == 1 # => true
|
||||
(1,) == 1 # => false
|
||||
(1) == 1 # => true
|
||||
|
||||
# Look how easy it is to swap two values
|
||||
e, d = d, e # => (5,4) # d is now 5 and e is now 4
|
||||
e, d = d, e # => (5,4) # d is now 5 and e is now 4
|
||||
|
||||
|
||||
# Dictionaries store mappings
|
||||
empty_dict = Dict() # => Dict{Any,Any}()
|
||||
empty_dict = Dict() # => Dict{Any,Any}()
|
||||
|
||||
# You can create a dictionary using a literal
|
||||
filled_dict = Dict("one"=> 1, "two"=> 2, "three"=> 3)
|
||||
# => Dict{ASCIIString,Int64}
|
||||
filled_dict = Dict("one" => 1, "two" => 2, "three" => 3)
|
||||
# => Dict{String,Int64}
|
||||
|
||||
# Look up values with []
|
||||
filled_dict["one"] # => 1
|
||||
filled_dict["one"] # => 1
|
||||
|
||||
# Get all keys
|
||||
keys(filled_dict)
|
||||
# => KeyIterator{Dict{ASCIIString,Int64}}(["three"=>3,"one"=>1,"two"=>2])
|
||||
# => Base.KeySet for a Dict{String,Int64} with 3 entries. Keys:
|
||||
# "two", "one", "three"
|
||||
# Note - dictionary keys are not sorted or in the order you inserted them.
|
||||
|
||||
# Get all values
|
||||
values(filled_dict)
|
||||
# => ValueIterator{Dict{ASCIIString,Int64}}(["three"=>3,"one"=>1,"two"=>2])
|
||||
# => Base.ValueIterator{Dict{String,Int64}} with 3 entries. Values: 2, 1, 3
|
||||
# Note - Same as above regarding key ordering.
|
||||
|
||||
# Check for existence of keys in a dictionary with in, haskey
|
||||
in(("one" => 1), filled_dict) # => true
|
||||
in(("two" => 3), filled_dict) # => false
|
||||
haskey(filled_dict, "one") # => true
|
||||
haskey(filled_dict, 1) # => false
|
||||
in(("one" => 1), filled_dict) # => true
|
||||
in(("two" => 3), filled_dict) # => false
|
||||
haskey(filled_dict, "one") # => true
|
||||
haskey(filled_dict, 1) # => false
|
||||
|
||||
# Trying to look up a non-existent key will raise an error
|
||||
try
|
||||
filled_dict["four"] # => ERROR: key not found: four in getindex at dict.jl:489
|
||||
filled_dict["four"] # => KeyError: key "four" not found
|
||||
catch e
|
||||
println(e)
|
||||
end
|
||||
|
||||
# Use the get method to avoid that error by providing a default value
|
||||
# get(dictionary,key,default_value)
|
||||
get(filled_dict,"one",4) # => 1
|
||||
get(filled_dict,"four",4) # => 4
|
||||
# get(dictionary, key, default_value)
|
||||
get(filled_dict, "one", 4) # => 1
|
||||
get(filled_dict, "four", 4) # => 4
|
||||
|
||||
# Use Sets to represent collections of unordered, unique values
|
||||
empty_set = Set() # => Set{Any}()
|
||||
empty_set = Set() # => Set{Any}()
|
||||
# Initialize a set with values
|
||||
filled_set = Set([1,2,2,3,4]) # => Set{Int64}(1,2,3,4)
|
||||
filled_set = Set([1, 2, 2, 3, 4]) # => Set([4, 2, 3, 1])
|
||||
|
||||
# Add more values to a set
|
||||
push!(filled_set,5) # => Set{Int64}(5,4,2,3,1)
|
||||
push!(filled_set, 5) # => Set([4, 2, 3, 5, 1])
|
||||
|
||||
# Check if the values are in the set
|
||||
in(2, filled_set) # => true
|
||||
in(10, filled_set) # => false
|
||||
in(2, filled_set) # => true
|
||||
in(10, filled_set) # => false
|
||||
|
||||
# There are functions for set intersection, union, and difference.
|
||||
other_set = Set([3, 4, 5, 6]) # => Set{Int64}(6,4,5,3)
|
||||
intersect(filled_set, other_set) # => Set{Int64}(3,4,5)
|
||||
union(filled_set, other_set) # => Set{Int64}(1,2,3,4,5,6)
|
||||
setdiff(Set([1,2,3,4]),Set([2,3,5])) # => Set{Int64}(1,4)
|
||||
other_set = Set([3, 4, 5, 6]) # => Set([4, 3, 5, 6])
|
||||
intersect(filled_set, other_set) # => Set([4, 3, 5])
|
||||
union(filled_set, other_set) # => Set([4, 2, 3, 5, 6, 1])
|
||||
setdiff(Set([1,2,3,4]), Set([2,3,5])) # => Set([4, 1])
|
||||
|
||||
|
||||
####################################################
|
||||
@ -337,7 +330,7 @@ end
|
||||
|
||||
# For loops iterate over iterables.
|
||||
# Iterable types include Range, Array, Set, Dict, and AbstractString.
|
||||
for animal=["dog", "cat", "mouse"]
|
||||
for animal = ["dog", "cat", "mouse"]
|
||||
println("$animal is a mammal")
|
||||
# You can use $ to interpolate variables or expression into strings
|
||||
end
|
||||
@ -355,15 +348,16 @@ end
|
||||
# cat is a mammal
|
||||
# mouse is a mammal
|
||||
|
||||
for a in Dict("dog"=>"mammal","cat"=>"mammal","mouse"=>"mammal")
|
||||
println("$(a[1]) is a $(a[2])")
|
||||
for pair in Dict("dog" => "mammal", "cat" => "mammal", "mouse" => "mammal")
|
||||
from, to = pair
|
||||
println("$from is a $to")
|
||||
end
|
||||
# prints:
|
||||
# dog is a mammal
|
||||
# cat is a mammal
|
||||
# mouse is a mammal
|
||||
|
||||
for (k,v) in Dict("dog"=>"mammal","cat"=>"mammal","mouse"=>"mammal")
|
||||
for (k, v) in Dict("dog" => "mammal", "cat" => "mammal", "mouse" => "mammal")
|
||||
println("$k is a $v")
|
||||
end
|
||||
# prints:
|
||||
@ -372,10 +366,11 @@ end
|
||||
# mouse is a mammal
|
||||
|
||||
# While loops loop while a condition is true
|
||||
x = 0
|
||||
while x < 4
|
||||
println(x)
|
||||
x += 1 # Shorthand for x = x + 1
|
||||
let x = 0
|
||||
while x < 4
|
||||
println(x)
|
||||
x += 1 # Shorthand for x = x + 1
|
||||
end
|
||||
end
|
||||
# prints:
|
||||
# 0
|
||||
@ -385,9 +380,9 @@ end
|
||||
|
||||
# Handle exceptions with a try/catch block
|
||||
try
|
||||
error("help")
|
||||
error("help")
|
||||
catch e
|
||||
println("caught it $e")
|
||||
println("caught it $e")
|
||||
end
|
||||
# => caught it ErrorException("help")
|
||||
|
||||
@ -407,15 +402,15 @@ function add(x, y)
|
||||
x + y
|
||||
end
|
||||
|
||||
add(5, 6) # => 11 after printing out "x is 5 and y is 6"
|
||||
add(5, 6) # => 11 after printing out "x is 5 and y is 6"
|
||||
|
||||
# Compact assignment of functions
|
||||
f_add(x, y) = x + y # => "f (generic function with 1 method)"
|
||||
f_add(3, 4) # => 7
|
||||
f_add(x, y) = x + y # => "f (generic function with 1 method)"
|
||||
f_add(3, 4) # => 7
|
||||
|
||||
# Function can also return multiple values as tuple
|
||||
fn(x, y) = x + y, x - y
|
||||
fn(3, 4) # => (7, -1)
|
||||
fn(3, 4) # => (7, -1)
|
||||
|
||||
# You can define functions that take a variable number of
|
||||
# positional arguments
|
||||
@ -425,41 +420,41 @@ function varargs(args...)
|
||||
end
|
||||
# => varargs (generic function with 1 method)
|
||||
|
||||
varargs(1,2,3) # => (1,2,3)
|
||||
varargs(1, 2, 3) # => (1,2,3)
|
||||
|
||||
# The ... is called a splat.
|
||||
# We just used it in a function definition.
|
||||
# It can also be used in a function call,
|
||||
# where it will splat an Array or Tuple's contents into the argument list.
|
||||
add([5,6]...) # this is equivalent to add(5,6)
|
||||
add([5,6]...) # this is equivalent to add(5,6)
|
||||
|
||||
x = (5,6) # => (5,6)
|
||||
add(x...) # this is equivalent to add(5,6)
|
||||
x = (5, 6) # => (5,6)
|
||||
add(x...) # this is equivalent to add(5,6)
|
||||
|
||||
|
||||
# You can define functions with optional positional arguments
|
||||
function defaults(a,b,x=5,y=6)
|
||||
function defaults(a, b, x=5, y=6)
|
||||
return "$a $b and $x $y"
|
||||
end
|
||||
|
||||
defaults('h','g') # => "h g and 5 6"
|
||||
defaults('h','g','j') # => "h g and j 6"
|
||||
defaults('h','g','j','k') # => "h g and j k"
|
||||
defaults('h', 'g') # => "h g and 5 6"
|
||||
defaults('h', 'g', 'j') # => "h g and j 6"
|
||||
defaults('h', 'g', 'j', 'k') # => "h g and j k"
|
||||
try
|
||||
defaults('h') # => ERROR: no method defaults(Char,)
|
||||
defaults() # => ERROR: no methods defaults()
|
||||
defaults('h') # => ERROR: no method defaults(Char,)
|
||||
defaults() # => ERROR: no methods defaults()
|
||||
catch e
|
||||
println(e)
|
||||
end
|
||||
|
||||
# You can define functions that take keyword arguments
|
||||
function keyword_args(;k1=4,name2="hello") # note the ;
|
||||
return Dict("k1"=>k1,"name2"=>name2)
|
||||
function keyword_args(;k1=4, name2="hello") # note the ;
|
||||
return Dict("k1" => k1, "name2" => name2)
|
||||
end
|
||||
|
||||
keyword_args(name2="ness") # => ["name2"=>"ness","k1"=>4]
|
||||
keyword_args(k1="mine") # => ["k1"=>"mine","name2"=>"hello"]
|
||||
keyword_args() # => ["name2"=>"hello","k1"=>4]
|
||||
keyword_args(name2="ness") # => ["name2"=>"ness","k1"=>4]
|
||||
keyword_args(k1="mine") # => ["k1"=>"mine","name2"=>"hello"]
|
||||
keyword_args() # => ["name2"=>"hello","k1"=>4]
|
||||
|
||||
# You can combine all kinds of arguments in the same function
|
||||
function all_the_args(normal_arg, optional_positional_arg=2; keyword_arg="foo")
|
||||
@ -483,7 +478,7 @@ function create_adder(x)
|
||||
end
|
||||
|
||||
# This is "stabby lambda syntax" for creating anonymous functions
|
||||
(x -> x > 2)(3) # => true
|
||||
(x -> x > 2)(3) # => true
|
||||
|
||||
# This function is identical to create_adder implementation above.
|
||||
function create_adder(x)
|
||||
@ -499,15 +494,15 @@ function create_adder(x)
|
||||
end
|
||||
|
||||
add_10 = create_adder(10)
|
||||
add_10(3) # => 13
|
||||
add_10(3) # => 13
|
||||
|
||||
|
||||
# There are built-in higher order functions
|
||||
map(add_10, [1,2,3]) # => [11, 12, 13]
|
||||
filter(x -> x > 5, [3, 4, 5, 6, 7]) # => [6, 7]
|
||||
map(add_10, [1,2,3]) # => [11, 12, 13]
|
||||
filter(x -> x > 5, [3, 4, 5, 6, 7]) # => [6, 7]
|
||||
|
||||
# We can use list comprehensions
|
||||
[add_10(i) for i=[1, 2, 3]] # => [11, 12, 13]
|
||||
[add_10(i) for i = [1, 2, 3]] # => [11, 12, 13]
|
||||
[add_10(i) for i in [1, 2, 3]] # => [11, 12, 13]
|
||||
[x for x in [3, 4, 5, 6, 7] if x > 5] # => [6, 7]
|
||||
|
||||
@ -518,11 +513,11 @@ filter(x -> x > 5, [3, 4, 5, 6, 7]) # => [6, 7]
|
||||
# Julia has a type system.
|
||||
# Every value has a type; variables do not have types themselves.
|
||||
# You can use the `typeof` function to get the type of a value.
|
||||
typeof(5) # => Int64
|
||||
typeof(5) # => Int64
|
||||
|
||||
# Types are first-class values
|
||||
typeof(Int64) # => DataType
|
||||
typeof(DataType) # => DataType
|
||||
typeof(Int64) # => DataType
|
||||
typeof(DataType) # => DataType
|
||||
# DataType is the type that represents types, including itself.
|
||||
|
||||
# Types are used for documentation, optimizations, and dispatch.
|
||||
@ -530,78 +525,77 @@ typeof(DataType) # => DataType
|
||||
|
||||
# Users can define types
|
||||
# They are like records or structs in other languages.
|
||||
# New types are defined using the `type` keyword.
|
||||
# New types are defined using the `struct` keyword.
|
||||
|
||||
# type Name
|
||||
# struct Name
|
||||
# field::OptionalType
|
||||
# ...
|
||||
# end
|
||||
type Tiger
|
||||
taillength::Float64
|
||||
coatcolor # not including a type annotation is the same as `::Any`
|
||||
struct Tiger
|
||||
taillength::Float64
|
||||
coatcolor # not including a type annotation is the same as `::Any`
|
||||
end
|
||||
|
||||
# The default constructor's arguments are the properties
|
||||
# of the type, in the order they are listed in the definition
|
||||
tigger = Tiger(3.5,"orange") # => Tiger(3.5,"orange")
|
||||
tigger = Tiger(3.5, "orange") # => Tiger(3.5,"orange")
|
||||
|
||||
# The type doubles as the constructor function for values of that type
|
||||
sherekhan = typeof(tigger)(5.6,"fire") # => Tiger(5.6,"fire")
|
||||
sherekhan = typeof(tigger)(5.6, "fire") # => Tiger(5.6,"fire")
|
||||
|
||||
# These struct-style types are called concrete types
|
||||
# They can be instantiated, but cannot have subtypes.
|
||||
# The other kind of types is abstract types.
|
||||
|
||||
# abstract Name
|
||||
abstract type Cat end # just a name and point in the type hierarchy
|
||||
abstract type Cat end # just a name and point in the type hierarchy
|
||||
|
||||
# Abstract types cannot be instantiated, but can have subtypes.
|
||||
using InteractiveUtils # defines the subtype and supertype function
|
||||
# For example, Number is an abstract type
|
||||
subtypes(Number) # => 2-element Array{Any,1}:
|
||||
subtypes(Number) # => 2-element Array{Any,1}:
|
||||
# Complex{T<:Real}
|
||||
# Real
|
||||
subtypes(Cat) # => 0-element Array{Any,1}
|
||||
subtypes(Cat) # => 0-element Array{Any,1}
|
||||
|
||||
# AbstractString, as the name implies, is also an abstract type
|
||||
subtypes(AbstractString) # 6-element Array{Union{DataType, UnionAll},1}:
|
||||
# Base.SubstitutionString
|
||||
# Base.Test.GenericString
|
||||
# DirectIndexString
|
||||
# RevString
|
||||
# String
|
||||
# SubString
|
||||
subtypes(AbstractString) # 4-element Array{Any,1}:
|
||||
# String
|
||||
# SubString
|
||||
# SubstitutionString
|
||||
# Test.GenericString
|
||||
|
||||
# Every type has a super type; use the `supertype` function to get it.
|
||||
typeof(5) # => Int64
|
||||
supertype(Int64) # => Signed
|
||||
supertype(Signed) # => Integer
|
||||
supertype(Integer) # => Real
|
||||
supertype(Real) # => Number
|
||||
supertype(Number) # => Any
|
||||
supertype(supertype(Signed)) # => Real
|
||||
supertype(Any) # => Any
|
||||
typeof(5) # => Int64
|
||||
supertype(Int64) # => Signed
|
||||
supertype(Signed) # => Integer
|
||||
supertype(Integer) # => Real
|
||||
supertype(Real) # => Number
|
||||
supertype(Number) # => Any
|
||||
supertype(supertype(Signed)) # => Real
|
||||
supertype(Any) # => Any
|
||||
# All of these type, except for Int64, are abstract.
|
||||
typeof("fire") # => String
|
||||
supertype(String) # => AbstractString
|
||||
typeof("fire") # => String
|
||||
supertype(String) # => AbstractString
|
||||
# Likewise here with String
|
||||
supertype(DirectIndexString) # => AbstractString
|
||||
supertype(SubString) # => AbstractString
|
||||
|
||||
# <: is the subtyping operator
|
||||
type Lion <: Cat # Lion is a subtype of Cat
|
||||
mane_color
|
||||
roar::AbstractString
|
||||
struct Lion <: Cat # Lion is a subtype of Cat
|
||||
mane_color
|
||||
roar::AbstractString
|
||||
end
|
||||
|
||||
# You can define more constructors for your type
|
||||
# Just define a function of the same name as the type
|
||||
# and call an existing constructor to get a value of the correct type
|
||||
Lion(roar::AbstractString) = Lion("green",roar)
|
||||
Lion(roar::AbstractString) = Lion("green", roar)
|
||||
# This is an outer constructor because it's outside the type definition
|
||||
|
||||
type Panther <: Cat # Panther is also a subtype of Cat
|
||||
eye_color
|
||||
Panther() = new("green")
|
||||
# Panthers will only have this constructor, and no default constructor.
|
||||
struct Panther <: Cat # Panther is also a subtype of Cat
|
||||
eye_color
|
||||
Panther() = new("green")
|
||||
# Panthers will only have this constructor, and no default constructor.
|
||||
end
|
||||
# Using inner constructors, like Panther does, gives you control
|
||||
# over how values of the type can be created.
|
||||
@ -619,35 +613,35 @@ end
|
||||
|
||||
# Definitions for Lion, Panther, Tiger
|
||||
function meow(animal::Lion)
|
||||
animal.roar # access type properties using dot notation
|
||||
animal.roar # access type properties using dot notation
|
||||
end
|
||||
|
||||
function meow(animal::Panther)
|
||||
"grrr"
|
||||
"grrr"
|
||||
end
|
||||
|
||||
function meow(animal::Tiger)
|
||||
"rawwwr"
|
||||
"rawwwr"
|
||||
end
|
||||
|
||||
# Testing the meow function
|
||||
meow(tigger) # => "rawwr"
|
||||
meow(Lion("brown","ROAAR")) # => "ROAAR"
|
||||
meow(Panther()) # => "grrr"
|
||||
meow(tigger) # => "rawwr"
|
||||
meow(Lion("brown", "ROAAR")) # => "ROAAR"
|
||||
meow(Panther()) # => "grrr"
|
||||
|
||||
# Review the local type hierarchy
|
||||
issubtype(Tiger,Cat) # => false
|
||||
issubtype(Lion,Cat) # => true
|
||||
issubtype(Panther,Cat) # => true
|
||||
Tiger <: Cat # => false
|
||||
Lion <: Cat # => true
|
||||
Panther <: Cat # => true
|
||||
|
||||
# Defining a function that takes Cats
|
||||
function pet_cat(cat::Cat)
|
||||
println("The cat says $(meow(cat))")
|
||||
println("The cat says $(meow(cat))")
|
||||
end
|
||||
|
||||
pet_cat(Lion("42")) # => prints "The cat says 42"
|
||||
pet_cat(Lion("42")) # => prints "The cat says 42"
|
||||
try
|
||||
pet_cat(tigger) # => ERROR: no method pet_cat(Tiger,)
|
||||
pet_cat(tigger) # => ERROR: no method pet_cat(Tiger,)
|
||||
catch e
|
||||
println(e)
|
||||
end
|
||||
@ -657,129 +651,132 @@ end
|
||||
# In Julia, all of the argument types contribute to selecting the best method.
|
||||
|
||||
# Let's define a function with more arguments, so we can see the difference
|
||||
function fight(t::Tiger,c::Cat)
|
||||
println("The $(t.coatcolor) tiger wins!")
|
||||
function fight(t::Tiger, c::Cat)
|
||||
println("The $(t.coatcolor) tiger wins!")
|
||||
end
|
||||
# => fight (generic function with 1 method)
|
||||
|
||||
fight(tigger,Panther()) # => prints The orange tiger wins!
|
||||
fight(tigger,Lion("ROAR")) # => prints The orange tiger wins!
|
||||
fight(tigger, Panther()) # => prints The orange tiger wins!
|
||||
fight(tigger, Lion("ROAR")) # => prints The orange tiger wins!
|
||||
|
||||
# Let's change the behavior when the Cat is specifically a Lion
|
||||
fight(t::Tiger,l::Lion) = println("The $(l.mane_color)-maned lion wins!")
|
||||
fight(t::Tiger, l::Lion) = println("The $(l.mane_color)-maned lion wins!")
|
||||
# => fight (generic function with 2 methods)
|
||||
|
||||
fight(tigger,Panther()) # => prints The orange tiger wins!
|
||||
fight(tigger,Lion("ROAR")) # => prints The green-maned lion wins!
|
||||
fight(tigger, Panther()) # => prints The orange tiger wins!
|
||||
fight(tigger, Lion("ROAR")) # => prints The green-maned lion wins!
|
||||
|
||||
# We don't need a Tiger in order to fight
|
||||
fight(l::Lion,c::Cat) = println("The victorious cat says $(meow(c))")
|
||||
fight(l::Lion, c::Cat) = println("The victorious cat says $(meow(c))")
|
||||
# => fight (generic function with 3 methods)
|
||||
|
||||
fight(Lion("balooga!"),Panther()) # => prints The victorious cat says grrr
|
||||
fight(Lion("balooga!"), Panther()) # => prints The victorious cat says grrr
|
||||
try
|
||||
fight(Panther(),Lion("RAWR"))
|
||||
fight(Panther(), Lion("RAWR"))
|
||||
catch e
|
||||
println(e)
|
||||
# => MethodError(fight, (Panther("green"), Lion("green", "RAWR")), 0x000000000000557b)
|
||||
println(e)
|
||||
# => MethodError(fight, (Panther("green"), Lion("green", "RAWR")),
|
||||
# 0x000000000000557b)
|
||||
end
|
||||
|
||||
# Also let the cat go first
|
||||
fight(c::Cat,l::Lion) = println("The cat beats the Lion")
|
||||
fight(c::Cat, l::Lion) = println("The cat beats the Lion")
|
||||
|
||||
# This warning is because it's unclear which fight will be called in:
|
||||
try
|
||||
fight(Lion("RAR"),Lion("brown","rarrr")) # => prints The victorious cat says rarrr
|
||||
fight(Lion("RAR"), Lion("brown", "rarrr"))
|
||||
# => prints The victorious cat says rarrr
|
||||
catch e
|
||||
println(e)
|
||||
# => MethodError(fight, (Lion("green", "RAR"), Lion("brown", "rarrr")), 0x000000000000557c)
|
||||
println(e)
|
||||
# => MethodError(fight, (Lion("green", "RAR"), Lion("brown", "rarrr")),
|
||||
# 0x000000000000557c)
|
||||
end
|
||||
# The result may be different in other versions of Julia
|
||||
|
||||
fight(l::Lion,l2::Lion) = println("The lions come to a tie")
|
||||
fight(Lion("RAR"),Lion("brown","rarrr")) # => prints The lions come to a tie
|
||||
fight(l::Lion, l2::Lion) = println("The lions come to a tie")
|
||||
fight(Lion("RAR"), Lion("brown", "rarrr")) # => prints The lions come to a tie
|
||||
|
||||
|
||||
# Under the hood
|
||||
# You can take a look at the llvm and the assembly code generated.
|
||||
|
||||
square_area(l) = l * l # square_area (generic function with 1 method)
|
||||
square_area(l) = l * l # square_area (generic function with 1 method)
|
||||
|
||||
square_area(5) #25
|
||||
square_area(5) # => 25
|
||||
|
||||
# What happens when we feed square_area an integer?
|
||||
code_native(square_area, (Int32,))
|
||||
# .section __TEXT,__text,regular,pure_instructions
|
||||
# Filename: none
|
||||
# Source line: 1 # Prologue
|
||||
# push RBP
|
||||
# mov RBP, RSP
|
||||
# Source line: 1
|
||||
# movsxd RAX, EDI # Fetch l from memory?
|
||||
# imul RAX, RAX # Square l and store the result in RAX
|
||||
# pop RBP # Restore old base pointer
|
||||
# ret # Result will still be in RAX
|
||||
# .section __TEXT,__text,regular,pure_instructions
|
||||
# Filename: none
|
||||
# Source line: 1 # Prologue
|
||||
# push RBP
|
||||
# mov RBP, RSP
|
||||
# Source line: 1
|
||||
# movsxd RAX, EDI # Fetch l from memory?
|
||||
# imul RAX, RAX # Square l and store the result in RAX
|
||||
# pop RBP # Restore old base pointer
|
||||
# ret # Result will still be in RAX
|
||||
|
||||
code_native(square_area, (Float32,))
|
||||
# .section __TEXT,__text,regular,pure_instructions
|
||||
# Filename: none
|
||||
# Source line: 1
|
||||
# push RBP
|
||||
# mov RBP, RSP
|
||||
# Source line: 1
|
||||
# vmulss XMM0, XMM0, XMM0 # Scalar single precision multiply (AVX)
|
||||
# pop RBP
|
||||
# ret
|
||||
# .section __TEXT,__text,regular,pure_instructions
|
||||
# Filename: none
|
||||
# Source line: 1
|
||||
# push RBP
|
||||
# mov RBP, RSP
|
||||
# Source line: 1
|
||||
# vmulss XMM0, XMM0, XMM0 # Scalar single precision multiply (AVX)
|
||||
# pop RBP
|
||||
# ret
|
||||
|
||||
code_native(square_area, (Float64,))
|
||||
# .section __TEXT,__text,regular,pure_instructions
|
||||
# Filename: none
|
||||
# Source line: 1
|
||||
# push RBP
|
||||
# mov RBP, RSP
|
||||
# Source line: 1
|
||||
# vmulsd XMM0, XMM0, XMM0 # Scalar double precision multiply (AVX)
|
||||
# pop RBP
|
||||
# ret
|
||||
#
|
||||
# .section __TEXT,__text,regular,pure_instructions
|
||||
# Filename: none
|
||||
# Source line: 1
|
||||
# push RBP
|
||||
# mov RBP, RSP
|
||||
# Source line: 1
|
||||
# vmulsd XMM0, XMM0, XMM0 # Scalar double precision multiply (AVX)
|
||||
# pop RBP
|
||||
# ret
|
||||
#
|
||||
# Note that julia will use floating point instructions if any of the
|
||||
# arguments are floats.
|
||||
# Let's calculate the area of a circle
|
||||
circle_area(r) = pi * r * r # circle_area (generic function with 1 method)
|
||||
circle_area(5) # 78.53981633974483
|
||||
circle_area(5) # 78.53981633974483
|
||||
|
||||
code_native(circle_area, (Int32,))
|
||||
# .section __TEXT,__text,regular,pure_instructions
|
||||
# Filename: none
|
||||
# Source line: 1
|
||||
# push RBP
|
||||
# mov RBP, RSP
|
||||
# Source line: 1
|
||||
# vcvtsi2sd XMM0, XMM0, EDI # Load integer (r) from memory
|
||||
# movabs RAX, 4593140240 # Load pi
|
||||
# vmulsd XMM1, XMM0, QWORD PTR [RAX] # pi * r
|
||||
# vmulsd XMM0, XMM0, XMM1 # (pi * r) * r
|
||||
# pop RBP
|
||||
# ret
|
||||
#
|
||||
# .section __TEXT,__text,regular,pure_instructions
|
||||
# Filename: none
|
||||
# Source line: 1
|
||||
# push RBP
|
||||
# mov RBP, RSP
|
||||
# Source line: 1
|
||||
# vcvtsi2sd XMM0, XMM0, EDI # Load integer (r) from memory
|
||||
# movabs RAX, 4593140240 # Load pi
|
||||
# vmulsd XMM1, XMM0, QWORD PTR [RAX] # pi * r
|
||||
# vmulsd XMM0, XMM0, XMM1 # (pi * r) * r
|
||||
# pop RBP
|
||||
# ret
|
||||
#
|
||||
|
||||
code_native(circle_area, (Float64,))
|
||||
# .section __TEXT,__text,regular,pure_instructions
|
||||
# Filename: none
|
||||
# Source line: 1
|
||||
# push RBP
|
||||
# mov RBP, RSP
|
||||
# movabs RAX, 4593140496
|
||||
# Source line: 1
|
||||
# vmulsd XMM1, XMM0, QWORD PTR [RAX]
|
||||
# vmulsd XMM0, XMM1, XMM0
|
||||
# pop RBP
|
||||
# ret
|
||||
#
|
||||
# .section __TEXT,__text,regular,pure_instructions
|
||||
# Filename: none
|
||||
# Source line: 1
|
||||
# push RBP
|
||||
# mov RBP, RSP
|
||||
# movabs RAX, 4593140496
|
||||
# Source line: 1
|
||||
# vmulsd XMM1, XMM0, QWORD PTR [RAX]
|
||||
# vmulsd XMM0, XMM1, XMM0
|
||||
# pop RBP
|
||||
# ret
|
||||
#
|
||||
```
|
||||
|
||||
## Further Reading
|
||||
|
||||
You can get a lot more detail from [The Julia Manual](http://docs.julialang.org/en/latest/#Manual-1)
|
||||
You can get a lot more detail from the [Julia Documentation](https://docs.julialang.org/)
|
||||
|
||||
The best place to get help with Julia is the (very friendly) [Discourse forum](https://discourse.julialang.org/).
|
||||
|
||||
Loading…
Reference in New Issue
Block a user