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Merge pull request #655 from jcouyang/master
[julia/zh-cn] Chinese translation for Julia
This commit is contained in:
Nami-Doc
commit
5b3a24af47
729
zh-cn/julia-cn.html.markdown
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729
zh-cn/julia-cn.html.markdown
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@ -0,0 +1,729 @@
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---
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language: julia
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filename: learn-julia-zh.jl
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contributors:
|
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- ["Jichao Ouyang", "http://oyanglul.us"]
|
||||
translators:
|
||||
- ["Jichao Ouyang"]
|
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lang: zh-cn
|
||||
---
|
||||
|
||||
```julia
|
||||
# 单行注释只需要一个井号
|
||||
#= 多行注释
|
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只需要以 '#=' 开始 '=#' 结束
|
||||
还可以嵌套.
|
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=#
|
||||
|
||||
####################################################
|
||||
## 1. 原始类型与操作符
|
||||
####################################################
|
||||
|
||||
# Julia 中一切皆是表达式。
|
||||
|
||||
# 这是一些基本数字类型.
|
||||
3 # => 3 (Int64)
|
||||
3.2 # => 3.2 (Float64)
|
||||
2 + 1im # => 2 + 1im (Complex{Int64})
|
||||
2//3 # => 2//3 (Rational{Int64})
|
||||
|
||||
# 支持所有的普通中缀操作符。
|
||||
1 + 1 # => 2
|
||||
8 - 1 # => 7
|
||||
10 * 2 # => 20
|
||||
35 / 5 # => 7.0
|
||||
5 / 2 # => 2.5 # 用 Int 除 Int 永远返回 Float
|
||||
div(5, 2) # => 2 # 使用 div 截断小数点
|
||||
5 \ 35 # => 7.0
|
||||
2 ^ 2 # => 4 # 次方, 不是二进制 xor
|
||||
12 % 10 # => 2
|
||||
|
||||
# 用括号提高优先级
|
||||
(1 + 3) * 2 # => 8
|
||||
|
||||
# 二进制操作符
|
||||
~2 # => -3 # 非
|
||||
3 & 5 # => 1 # 与
|
||||
2 | 4 # => 6 # 或
|
||||
2 $ 4 # => 6 # 异或
|
||||
2 >>> 1 # => 1 # 逻辑右移
|
||||
2 >> 1 # => 1 # 算术右移
|
||||
2 << 1 # => 4 # 逻辑/算术 右移
|
||||
|
||||
# 可以用函数 bits 查看二进制数。
|
||||
bits(12345)
|
||||
# => "0000000000000000000000000000000000000000000000000011000000111001"
|
||||
bits(12345.0)
|
||||
# => "0100000011001000000111001000000000000000000000000000000000000000"
|
||||
|
||||
# 布尔值是原始类型
|
||||
true
|
||||
false
|
||||
|
||||
# 布尔操作符
|
||||
!true # => false
|
||||
!false # => true
|
||||
1 == 1 # => true
|
||||
2 == 1 # => false
|
||||
1 != 1 # => false
|
||||
2 != 1 # => true
|
||||
1 < 10 # => true
|
||||
1 > 10 # => false
|
||||
2 <= 2 # => true
|
||||
2 >= 2 # => true
|
||||
# 比较可以串联
|
||||
1 < 2 < 3 # => true
|
||||
2 < 3 < 2 # => false
|
||||
|
||||
# 字符串可以由 " 创建
|
||||
"This is a string."
|
||||
|
||||
# 字符字面量可用 ' 创建
|
||||
'a'
|
||||
|
||||
# 可以像取数组取值一样用 index 取出对应字符
|
||||
"This is a string"[1] # => 'T' # Julia 的 index 从 1 开始 :(
|
||||
# 但是对 UTF-8 无效,
|
||||
# 因此建议使用遍历器 (map, for loops, 等).
|
||||
|
||||
# $ 可用于字符插值:
|
||||
"2 + 2 = $(2 + 2)" # => "2 + 2 = 4"
|
||||
# 可以将任何 Julia 表达式放入括号。
|
||||
|
||||
# 另一种格式化字符串的方式是 printf 宏.
|
||||
@printf "%d is less than %f" 4.5 5.3 # 5 is less than 5.300000
|
||||
|
||||
# 打印字符串很容易
|
||||
println("I'm Julia. Nice to meet you!")
|
||||
|
||||
####################################################
|
||||
## 2. 变量与集合
|
||||
####################################################
|
||||
|
||||
# 给变量赋值就是声明变量
|
||||
some_var = 5 # => 5
|
||||
some_var # => 5
|
||||
|
||||
# 访问未声明变量会抛出异常
|
||||
try
|
||||
some_other_var # => ERROR: some_other_var not defined
|
||||
catch e
|
||||
println(e)
|
||||
end
|
||||
|
||||
# 变量名需要以字母开头.
|
||||
# 之后任何字母，数字，下划线，叹号都是合法的。
|
||||
SomeOtherVar123! = 6 # => 6
|
||||
|
||||
# 甚至可以用 unicode 字符
|
||||
☃ = 8 # => 8
|
||||
# 用数学符号非常方便
|
||||
2 * π # => 6.283185307179586
|
||||
|
||||
# 注意 Julia 的命名规约:
|
||||
#
|
||||
# * 变量名为小写，单词之间以下划线连接('\_')。
|
||||
#
|
||||
# * 类型名以大写字母开头，单词以 CamelCase 方式连接。
|
||||
#
|
||||
# * 函数与宏的名字小写，无下划线。
|
||||
#
|
||||
# * 会改变输入的函数名末位为 !。
|
||||
# 这类函数有时被称为 mutating functions 或 in-place functions.
|
||||
|
||||
# 数组存储一列值，index 从 1 开始。
|
||||
a = Int64[] # => 0-element Int64 Array
|
||||
|
||||
# 一维数组可以以逗号分隔值的方式声明。
|
||||
b = [4, 5, 6] # => 包含 3 个 Int64 类型元素的数组: [4, 5, 6]
|
||||
b[1] # => 4
|
||||
b[end] # => 6
|
||||
|
||||
# 二维数组以分号分隔维度。
|
||||
matrix = [1 2; 3 4] # => 2x2 Int64 数组: [1 2; 3 4]
|
||||
|
||||
# 使用 push! 和 append! 往数组末尾添加元素
|
||||
push!(a,1) # => [1]
|
||||
push!(a,2) # => [1,2]
|
||||
push!(a,4) # => [1,2,4]
|
||||
push!(a,3) # => [1,2,4,3]
|
||||
append!(a,b) # => [1,2,4,3,4,5,6]
|
||||
|
||||
# 用 pop 弹出末尾元素
|
||||
pop!(b) # => 6 and b is now [4,5]
|
||||
|
||||
# 可以再放回去
|
||||
push!(b,6) # b 又变成了 [4,5,6].
|
||||
|
||||
a[1] # => 1 # 永远记住 Julia 的 index 从 1 开始!
|
||||
|
||||
# 用 end 可以直接取到最后索引. 可用作任何索引表达式
|
||||
a[end] # => 6
|
||||
|
||||
# 还支持 shift 和 unshift
|
||||
shift!(a) # => 返回 1，而 a 现在时 [2,4,3,4,5,6]
|
||||
unshift!(a,7) # => [7,2,4,3,4,5,6]
|
||||
|
||||
# 以叹号结尾的函数名表示它会改变参数的值
|
||||
arr = [5,4,6] # => 包含三个 Int64 元素的数组: [5,4,6]
|
||||
sort(arr) # => [4,5,6]; arr 还是 [5,4,6]
|
||||
sort!(arr) # => [4,5,6]; arr 现在是 [4,5,6]
|
||||
|
||||
# 越界会抛出 BoundsError 异常
|
||||
try
|
||||
a[0] # => ERROR: BoundsError() in getindex at array.jl:270
|
||||
a[end+1] # => ERROR: BoundsError() in getindex at array.jl:270
|
||||
catch e
|
||||
println(e)
|
||||
end
|
||||
|
||||
# 错误会指出发生的行号，包括标准库
|
||||
# 如果你有 Julia 源代码，你可以找到这些地方
|
||||
|
||||
# 可以用 range 初始化数组
|
||||
a = [1:5] # => 5-element Int64 Array: [1,2,3,4,5]
|
||||
|
||||
# 可以切割数组
|
||||
a[1:3] # => [1, 2, 3]
|
||||
a[2:end] # => [2, 3, 4, 5]
|
||||
|
||||
# 用 splice! 切割原数组
|
||||
arr = [3,4,5]
|
||||
splice!(arr,2) # => 4 ; arr 变成了 [3,5]
|
||||
|
||||
# 用 append! 连接数组
|
||||
b = [1,2,3]
|
||||
append!(a,b) # a 变成了 [1, 2, 3, 4, 5, 1, 2, 3]
|
||||
|
||||
# 检查元素是否在数组中
|
||||
in(1, a) # => true
|
||||
|
||||
# 用 length 获得数组长度
|
||||
length(a) # => 8
|
||||
|
||||
# Tuples 是 immutable 的
|
||||
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
|
||||
|
||||
# 大多数组的函数同样支持 tuples
|
||||
length(tup) # => 3
|
||||
tup[1:2] # => (1,2)
|
||||
in(2, tup) # => true
|
||||
|
||||
# 可以将 tuples 元素分别赋给变量
|
||||
a, b, c = (1, 2, 3) # => (1,2,3) # a is now 1, b is now 2 and c is now 3
|
||||
|
||||
# 不用括号也可以
|
||||
d, e, f = 4, 5, 6 # => (4,5,6)
|
||||
|
||||
# 单元素 tuple 不等于其元素值
|
||||
(1,) == 1 # => false
|
||||
(1) == 1 # => true
|
||||
|
||||
# 交换值
|
||||
e, d = d, e # => (5,4) # d is now 5 and e is now 4
|
||||
|
||||
|
||||
# 字典Dictionaries store mappings
|
||||
empty_dict = Dict() # => Dict{Any,Any}()
|
||||
|
||||
# 也可以用字面量创建字典
|
||||
filled_dict = ["one"=> 1, "two"=> 2, "three"=> 3]
|
||||
# => Dict{ASCIIString,Int64}
|
||||
|
||||
# 用 [] 获得键值
|
||||
filled_dict["one"] # => 1
|
||||
|
||||
# 获得所有键
|
||||
keys(filled_dict)
|
||||
# => KeyIterator{Dict{ASCIIString,Int64}}(["three"=>3,"one"=>1,"two"=>2])
|
||||
# 注意，键的顺序不是插入时的顺序
|
||||
|
||||
# 获得所有值
|
||||
values(filled_dict)
|
||||
# => ValueIterator{Dict{ASCIIString,Int64}}(["three"=>3,"one"=>1,"two"=>2])
|
||||
# 注意，值的顺序也一样
|
||||
|
||||
# 用 in 检查键值是否已存在，用 haskey 检查键是否存在
|
||||
in(("one", 1), filled_dict) # => true
|
||||
in(("two", 3), filled_dict) # => false
|
||||
haskey(filled_dict, "one") # => true
|
||||
haskey(filled_dict, 1) # => false
|
||||
|
||||
# 获取不存在的键的值会抛出异常
|
||||
try
|
||||
filled_dict["four"] # => ERROR: key not found: four in getindex at dict.jl:489
|
||||
catch e
|
||||
println(e)
|
||||
end
|
||||
|
||||
# 使用 get 可以提供默认值来避免异常
|
||||
# get(dictionary,key,default_value)
|
||||
get(filled_dict,"one",4) # => 1
|
||||
get(filled_dict,"four",4) # => 4
|
||||
|
||||
# 用 Sets 表示无序不可重复的值的集合
|
||||
empty_set = Set() # => Set{Any}()
|
||||
# 初始化一个 Set 并定义其值
|
||||
filled_set = Set(1,2,2,3,4) # => Set{Int64}(1,2,3,4)
|
||||
|
||||
# 添加值
|
||||
push!(filled_set,5) # => Set{Int64}(5,4,2,3,1)
|
||||
|
||||
# 检查是否存在某值
|
||||
in(2, filled_set) # => true
|
||||
in(10, filled_set) # => false
|
||||
|
||||
# 交集，并集，差集
|
||||
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)
|
||||
|
||||
|
||||
####################################################
|
||||
## 3. 控制流
|
||||
####################################################
|
||||
|
||||
# 声明一个变量
|
||||
some_var = 5
|
||||
|
||||
# 这是一个 if 语句，缩进不是必要的
|
||||
if some_var > 10
|
||||
println("some_var is totally bigger than 10.")
|
||||
elseif some_var < 10 # elseif 是可选的.
|
||||
println("some_var is smaller than 10.")
|
||||
else # else 也是可选的.
|
||||
println("some_var is indeed 10.")
|
||||
end
|
||||
# => prints "some var is smaller than 10"
|
||||
|
||||
|
||||
# For 循环遍历
|
||||
# Iterable 类型包括 Range, Array, Set, Dict, 以及 String.
|
||||
for animal=["dog", "cat", "mouse"]
|
||||
println("$animal is a mammal")
|
||||
# 可用 $ 将 variables 或 expression 转换为字符串into strings
|
||||
end
|
||||
# prints:
|
||||
# dog is a mammal
|
||||
# cat is a mammal
|
||||
# mouse is a mammal
|
||||
|
||||
# You can use 'in' instead of '='.
|
||||
for animal in ["dog", "cat", "mouse"]
|
||||
println("$animal is a mammal")
|
||||
end
|
||||
# prints:
|
||||
# dog is a mammal
|
||||
# cat is a mammal
|
||||
# mouse is a mammal
|
||||
|
||||
for a in ["dog"=>"mammal","cat"=>"mammal","mouse"=>"mammal"]
|
||||
println("$(a[1]) is a $(a[2])")
|
||||
end
|
||||
# prints:
|
||||
# dog is a mammal
|
||||
# cat is a mammal
|
||||
# mouse is a mammal
|
||||
|
||||
for (k,v) in ["dog"=>"mammal","cat"=>"mammal","mouse"=>"mammal"]
|
||||
println("$k is a $v")
|
||||
end
|
||||
# prints:
|
||||
# dog is a mammal
|
||||
# cat is a mammal
|
||||
# mouse is a mammal
|
||||
|
||||
# While 循环
|
||||
x = 0
|
||||
while x < 4
|
||||
println(x)
|
||||
x += 1 # x = x + 1
|
||||
end
|
||||
# prints:
|
||||
# 0
|
||||
# 1
|
||||
# 2
|
||||
# 3
|
||||
|
||||
# 用 try/catch 处理异常
|
||||
try
|
||||
error("help")
|
||||
catch e
|
||||
println("caught it $e")
|
||||
end
|
||||
# => caught it ErrorException("help")
|
||||
|
||||
|
||||
####################################################
|
||||
## 4. 函数
|
||||
####################################################
|
||||
|
||||
# 用关键字 'function' 可创建一个新函数
|
||||
#function name(arglist)
|
||||
# body...
|
||||
#end
|
||||
function add(x, y)
|
||||
println("x is $x and y is $y")
|
||||
|
||||
# 最后一行语句的值为返回
|
||||
x + y
|
||||
end
|
||||
|
||||
add(5, 6) # => 在 "x is 5 and y is 6" 后会打印 11
|
||||
|
||||
# 还可以定义接收可变长参数的函数
|
||||
function varargs(args...)
|
||||
return args
|
||||
# 关键字 return 可在函数内部任何地方返回
|
||||
end
|
||||
# => varargs (generic function with 1 method)
|
||||
|
||||
varargs(1,2,3) # => (1,2,3)
|
||||
|
||||
# 省略号 ... 被称为 splat.
|
||||
# 刚刚用在了函数定义中
|
||||
# 还可以用在函数的调用
|
||||
# Array 或者 Tuple 的内容会变成参数列表
|
||||
Set([1,2,3]) # => Set{Array{Int64,1}}([1,2,3]) # 获得一个 Array 的 Set
|
||||
Set([1,2,3]...) # => Set{Int64}(1,2,3) # 相当于 Set(1,2,3)
|
||||
|
||||
x = (1,2,3) # => (1,2,3)
|
||||
Set(x) # => Set{(Int64,Int64,Int64)}((1,2,3)) # 一个 Tuple 的 Set
|
||||
Set(x...) # => Set{Int64}(2,3,1)
|
||||
|
||||
|
||||
# 可定义可选参数的函数
|
||||
function defaults(a,b,x=5,y=6)
|
||||
return "$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"
|
||||
try
|
||||
defaults('h') # => ERROR: no method defaults(Char,)
|
||||
defaults() # => ERROR: no methods defaults()
|
||||
catch e
|
||||
println(e)
|
||||
end
|
||||
|
||||
# 还可以定义键值对的参数
|
||||
function keyword_args(;k1=4,name2="hello") # note the ;
|
||||
return ["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]
|
||||
|
||||
# 可以组合各种类型的参数在同一个函数的参数列表中
|
||||
function all_the_args(normal_arg, optional_positional_arg=2; keyword_arg="foo")
|
||||
println("normal arg: $normal_arg")
|
||||
println("optional arg: $optional_positional_arg")
|
||||
println("keyword arg: $keyword_arg")
|
||||
end
|
||||
|
||||
all_the_args(1, 3, keyword_arg=4)
|
||||
# prints:
|
||||
# normal arg: 1
|
||||
# optional arg: 3
|
||||
# keyword arg: 4
|
||||
|
||||
# Julia 有一等函数
|
||||
function create_adder(x)
|
||||
adder = function (y)
|
||||
return x + y
|
||||
end
|
||||
return adder
|
||||
end
|
||||
|
||||
# 这是用 "stabby lambda syntax" 创建的匿名函数
|
||||
(x -> x > 2)(3) # => true
|
||||
|
||||
# 这个函数和上面的 create_adder 一模一样
|
||||
function create_adder(x)
|
||||
y -> x + y
|
||||
end
|
||||
|
||||
# 你也可以给内部函数起个名字
|
||||
function create_adder(x)
|
||||
function adder(y)
|
||||
x + y
|
||||
end
|
||||
adder
|
||||
end
|
||||
|
||||
add_10 = create_adder(10)
|
||||
add_10(3) # => 13
|
||||
|
||||
|
||||
# 内置的高阶函数有
|
||||
map(add_10, [1,2,3]) # => [11, 12, 13]
|
||||
filter(x -> x > 5, [3, 4, 5, 6, 7]) # => [6, 7]
|
||||
|
||||
# 还可以使用 list comprehensions 替代 map
|
||||
[add_10(i) for i=[1, 2, 3]] # => [11, 12, 13]
|
||||
[add_10(i) for i in [1, 2, 3]] # => [11, 12, 13]
|
||||
|
||||
####################################################
|
||||
## 5. 类型
|
||||
####################################################
|
||||
|
||||
# Julia 有类型系统
|
||||
# 所有的值都有类型；但变量本身没有类型
|
||||
# 你可以用 `typeof` 函数获得值的类型
|
||||
typeof(5) # => Int64
|
||||
|
||||
# 类型是一等值
|
||||
typeof(Int64) # => DataType
|
||||
typeof(DataType) # => DataType
|
||||
# DataType 是代表类型的类型，也代表他自己的类型
|
||||
|
||||
# 类型可用作文档化，优化，以及调度
|
||||
# 并不是静态检查类型
|
||||
|
||||
# 用户还可以自定义类型
|
||||
# 跟其他语言的 records 或 structs 一样
|
||||
# 用 `type` 关键字定义新的类型
|
||||
|
||||
# type Name
|
||||
# field::OptionalType
|
||||
# ...
|
||||
# end
|
||||
type Tiger
|
||||
taillength::Float64
|
||||
coatcolor # 不附带类型标注的相当于 `::Any`
|
||||
end
|
||||
|
||||
# 构造函数参数是类型的属性
|
||||
tigger = Tiger(3.5,"orange") # => Tiger(3.5,"orange")
|
||||
|
||||
# 用新类型作为构造函数还会创建一个类型
|
||||
sherekhan = typeof(tigger)(5.6,"fire") # => Tiger(5.6,"fire")
|
||||
|
||||
# struct 类似的类型被称为具体类型
|
||||
# 他们可被实例化但不能有子类型
|
||||
# 另一种类型是抽象类型
|
||||
|
||||
# abstract Name
|
||||
abstract Cat # just a name and point in the type hierarchy
|
||||
|
||||
# 抽象类型不能被实例化，但是可以有子类型
|
||||
# 例如，Number 就是抽象类型
|
||||
subtypes(Number) # => 6-element Array{Any,1}:
|
||||
# Complex{Float16}
|
||||
# Complex{Float32}
|
||||
# Complex{Float64}
|
||||
# Complex{T<:Real}
|
||||
# ImaginaryUnit
|
||||
# Real
|
||||
subtypes(Cat) # => 0-element Array{Any,1}
|
||||
|
||||
# 所有的类型都有父类型; 可以用函数 `super` 得到父类型.
|
||||
typeof(5) # => Int64
|
||||
super(Int64) # => Signed
|
||||
super(Signed) # => Real
|
||||
super(Real) # => Number
|
||||
super(Number) # => Any
|
||||
super(super(Signed)) # => Number
|
||||
super(Any) # => Any
|
||||
# 所有这些类型，除了 Int64, 都是抽象类型.
|
||||
|
||||
# <: 是类型集成操作符
|
||||
type Lion <: Cat # Lion 是 Cat 的子类型
|
||||
mane_color
|
||||
roar::String
|
||||
end
|
||||
|
||||
# 可以继续为你的类型定义构造函数
|
||||
# 只需要定义一个同名的函数
|
||||
# 并调用已有的构造函数设置一个固定参数
|
||||
Lion(roar::String) = Lion("green",roar)
|
||||
# 这是一个外部构造函数，因为他再类型定义之外
|
||||
|
||||
type Panther <: Cat # Panther 也是 Cat 的子类型
|
||||
eye_color
|
||||
Panther() = new("green")
|
||||
# Panthers 只有这个构造函数，没有默认构造函数
|
||||
end
|
||||
# 使用内置构造函数，如 Panther，可以让你控制
|
||||
# 如何构造类型的值
|
||||
# 应该尽可能使用外部构造函数而不是内部构造函数
|
||||
|
||||
####################################################
|
||||
## 6. 多分派
|
||||
####################################################
|
||||
|
||||
# 在Julia中, 所有的具名函数都是类属函数
|
||||
# 这意味着他们都是有很大小方法组成的
|
||||
# 每个 Lion 的构造函数都是类属函数 Lion 的方法
|
||||
|
||||
# 我们来看一个非构造函数的例子
|
||||
|
||||
# Lion, Panther, Tiger 的 meow 定义为
|
||||
function meow(animal::Lion)
|
||||
animal.roar # 使用点符号访问属性
|
||||
end
|
||||
|
||||
function meow(animal::Panther)
|
||||
"grrr"
|
||||
end
|
||||
|
||||
function meow(animal::Tiger)
|
||||
"rawwwr"
|
||||
end
|
||||
|
||||
# 试试 meow 函数
|
||||
meow(tigger) # => "rawwr"
|
||||
meow(Lion("brown","ROAAR")) # => "ROAAR"
|
||||
meow(Panther()) # => "grrr"
|
||||
|
||||
# 再看看层次结构
|
||||
issubtype(Tiger,Cat) # => false
|
||||
issubtype(Lion,Cat) # => true
|
||||
issubtype(Panther,Cat) # => true
|
||||
|
||||
# 定义一个接收 Cats 的函数
|
||||
function pet_cat(cat::Cat)
|
||||
println("The cat says $(meow(cat))")
|
||||
end
|
||||
|
||||
pet_cat(Lion("42")) # => prints "The cat says 42"
|
||||
try
|
||||
pet_cat(tigger) # => ERROR: no method pet_cat(Tiger,)
|
||||
catch e
|
||||
println(e)
|
||||
end
|
||||
|
||||
# 在面向对象语言中，通常都是单分派
|
||||
# 这意味着分派方法是通过第一个参数的类型决定的
|
||||
# 在Julia中, 所有参数类型都会被考虑到
|
||||
|
||||
# 让我们定义有多个参数的函数，好看看区别
|
||||
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!
|
||||
|
||||
# 让我们修改一下传入具体为 Lion 类型时的行为
|
||||
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!
|
||||
|
||||
# 把 Tiger 去掉
|
||||
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
|
||||
try
|
||||
fight(Panther(),Lion("RAWR")) # => ERROR: no method fight(Panther,Lion)
|
||||
catch
|
||||
end
|
||||
|
||||
# 在试试让 Cat 在前面
|
||||
fight(c::Cat,l::Lion) = println("The cat beats the Lion")
|
||||
# => Warning: New definition
|
||||
# fight(Cat,Lion) at none:1
|
||||
# is ambiguous with
|
||||
# fight(Lion,Cat) at none:2.
|
||||
# Make sure
|
||||
# fight(Lion,Lion)
|
||||
# is defined first.
|
||||
#fight (generic function with 4 methods)
|
||||
|
||||
# 警告说明了无法判断使用哪个 fight 方法
|
||||
fight(Lion("RAR"),Lion("brown","rarrr")) # => prints The victorious cat says rarrr
|
||||
# 结果在老版本 Julia 中可能会不一样
|
||||
|
||||
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
|
||||
# 你还可以看看 llvm 以及生成的汇编代码
|
||||
|
||||
square_area(l) = l * l # square_area (generic function with 1 method)
|
||||
|
||||
square_area(5) #25
|
||||
|
||||
# 给 square_area 一个整形时发生什么
|
||||
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
|
||||
|
||||
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
|
||||
|
||||
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
|
||||
#
|
||||
# 注意 只要参数中又浮点类型，Julia 就使用浮点指令
|
||||
# 让我们计算一下圆的面积
|
||||
circle_area(r) = pi * r * r # circle_area (generic function with 1 method)
|
||||
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
|
||||
#
|
||||
|
||||
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
|
||||
#
|
||||
```
|
||||
Loading…
Reference in New Issue
Block a user