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865 lines
25 KiB
Julia
865 lines
25 KiB
Julia
---
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language: Julia
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filename: learn-julia-zh.jl
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contributors:
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- ["Leah Hanson", "http://leahhanson.us"]
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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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translators:
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- ["Jichao Ouyang", "http://oyanglul.us"]
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- ["woclass", "https://github.com/inkydragon"]
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lang: zh-cn
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---
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Julia 是一种新的同像函数式编程语言(homoiconic functional language)，它专注于科学计算领域。
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虽然拥有同像宏(homoiconic macros)、一级函数(first-class functions)和底层控制等全部功能，但 Julia 依旧和 Python 一样易于学习和使用。
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示例代码基于 Julia 1.0.0
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```julia
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# 单行注释只需要一个井号「#」
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#= 多行注释
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只需要以「#=」开始「=#」结束
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还可以嵌套.
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=#
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####################################################
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## 1. 原始类型与操作符
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####################################################
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# Julia 中一切皆为表达式
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# 这是一些基本数字类型
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typeof(3) # => Int64
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typeof(3.2) # => Float64
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typeof(2 + 1im) # => Complex{Int64}
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typeof(2 // 3) # => Rational{Int64}
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# 支持所有的普通中缀操作符
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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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10 / 2 # => 5.0 # 整数除法总是返回浮点数
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div(5, 2) # => 2 # 使用 div 可以获得整除的结果
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5 \ 35 # => 7.0
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2^2 # => 4 # 幂运算，不是异或 (xor)
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12 % 10 # => 2
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# 用括号提高优先级
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(1 + 3) * 2 # => 8
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# 位操作符
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~2 # => -3 # 按位非 (not)
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3 & 5 # => 1 # 按位与 (and)
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2 | 4 # => 6 # 按位或 (or)
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xor(2, 4) # => 6 # 按位异或 (xor)
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2 >>> 1 # => 1 # 逻辑右移
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2 >> 1 # => 1 # 算术右移
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2 << 1 # => 4 # 逻辑/算术左移
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# 可以用函数 bitstring 查看二进制数。
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bitstring(12345)
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# => "0000000000000000000000000000000000000000000000000011000000111001"
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bitstring(12345.0)
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# => "0100000011001000000111001000000000000000000000000000000000000000"
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# 布尔值是原始类型
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true
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false
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# 布尔操作符
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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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# 链式比较
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1 < 2 < 3 # => true
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2 < 3 < 2 # => false
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# 字符串可以由「"」创建
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"This is a string."
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# 字符字面量可用「'」创建
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'a'
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# 字符串使用 UTF-8 编码
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# 可以像取数组取值一样用 index 取出对应字符
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ascii("This is a string")[1]
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# => 'T': ASCII/Unicode U+0054 (category Lu: Letter, uppercase)
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# Julia 的 index 从 1 开始 :(
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# 但只有在字符串仅由 ASCII 字符构成时，字符串才能够被安全的引索
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# 因此建议使用遍历器 (map, for loops, 等)
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# $ 可用于字符插值:
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"2 + 2 = $(2 + 2)" # => "2 + 2 = 4"
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# 可以将任何 Julia 表达式放入括号。
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# 另一种输出格式化字符串的方法是使用标准库 Printf 中的 Printf 宏
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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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# 打印字符串很容易
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println("I'm Julia. Nice to meet you!") # => I'm Julia. Nice to meet you!
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# 字符串可以按字典序进行比较
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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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####################################################
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## 2. 变量与集合
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####################################################
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# 给变量赋值就是声明变量
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some_var = 5 # => 5
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some_var # => 5
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# 访问未声明变量会抛出异常
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try
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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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# 变量名必须以下划线或字母开头
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# 之后任何字母，数字，下划线，叹号都是合法的。
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SomeOtherVar123! = 6 # => 6
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# 甚至可以用 unicode 字符
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☃ = 8 # => 8
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# 用数学符号非常方便
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2 * π # => 6.283185307179586
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# 注意 Julia 的命名规约:
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#
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# * 名称可以用下划线「_」分割。
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# 不过一般不推荐使用下划线，除非不用变量名就会变得难于理解
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#
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# * 类型名以大写字母开头，单词以 CamelCase 方式连接，无下划线。
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#
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# * 函数与宏的名字小写，无下划线。
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#
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# * 会改变输入的函数名末位为「!」。
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# 这类函数有时被称为 mutating functions 或 in-place functions.
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# 数组存储一列值，index 从 1 开始
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a = Int64[] # => 0-element Array{Int64,1}
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# 一维数组可以以逗号分隔值的方式声明
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b = [4, 5, 6] # => 3-element Array{Int64,1}: [4, 5, 6]
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b = [4; 5; 6] # => 3-element Array{Int64,1}: [4, 5, 6]
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b[1] # => 4
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b[end] # => 6
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# 二维数组以分号分隔维度
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matrix = [1 2; 3 4] # => 2×2 Array{Int64,2}: [1 2; 3 4]
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# 指定数组的类型
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b = Int8[4, 5, 6] # => 3-element Array{Int8,1}: [4, 5, 6]
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# 使用 push! 和 append! 往数组末尾添加元素
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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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# 用 pop 弹出尾部的元素
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pop!(b) # => 6
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b # => [4,5]
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# 再放回去
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push!(b, 6) # => [4,5,6]
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b # => [4,5,6]
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a[1] # => 1 # 永远记住 Julia 的引索从 1 开始！而不是 0！
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# 用 end 可以直接取到最后索引。它可以用在任何索引表达式中
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a[end] # => 6
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# 数组还支持 popfirst! 和 pushfirst!
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popfirst!(a) # => 1
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a # => [2,4,3,4,5,6]
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pushfirst!(a, 7) # => [7,2,4,3,4,5,6]
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a # => [7,2,4,3,4,5,6]
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# 以叹号结尾的函数名表示它会改变参数的值
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arr = [5,4,6] # => 3-element Array{Int64,1}: [5,4,6]
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sort(arr) # => [4,5,6]
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arr # => [5,4,6]
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sort!(arr) # => [4,5,6]
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arr # => [4,5,6]
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# 数组越界会抛出 BoundsError
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try
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a[0]
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# => ERROR: BoundsError: attempt to access 7-element Array{Int64,1} at
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# index [0]
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# => Stacktrace:
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# => [1] getindex(::Array{Int64,1}, ::Int64) at .\array.jl:731
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# => [2] top-level scope at none:0
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# => [3] ...
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# => in expression starting at ...\LearnJulia.jl:203
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a[end + 1]
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# => ERROR: BoundsError: attempt to access 7-element Array{Int64,1} at
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# index [8]
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# => Stacktrace:
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# => [1] getindex(::Array{Int64,1}, ::Int64) at .\array.jl:731
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# => [2] top-level scope at none:0
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# => [3] ...
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# => in expression starting at ...\LearnJulia.jl:211
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catch e
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println(e)
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end
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# 报错时错误会指出出错的文件位置以及行号，标准库也一样
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# 你可以在 Julia 安装目录下的 share/julia 文件夹里找到这些标准库
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# 可以用 range 初始化数组
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a = [1:5;] # => 5-element Array{Int64,1}: [1,2,3,4,5]
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# 注意！分号不可省略
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a2 = [1:5] # => 1-element Array{UnitRange{Int64},1}: [1:5]
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# 可以切割数组
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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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# 用 splice! 切割原数组
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arr = [3,4,5]
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splice!(arr, 2) # => 4
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arr # => [3,5]
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# 用 append! 连接数组
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b = [1,2,3]
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append!(a, b) # => [1, 2, 3, 4, 5, 1, 2, 3]
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a # => [1, 2, 3, 4, 5, 1, 2, 3]
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# 检查元素是否在数组中
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in(1, a) # => true
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# 用 length 获得数组长度
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length(a) # => 8
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# 元组(Tuples)是不可变的
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tup = (1, 2, 3) # => (1,2,3)
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typeof(tup) # => Tuple{Int64,Int64,Int64}
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tup[1] # => 1
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try
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tup[1] = 3
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# => ERROR: MethodError: no method matching
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# setindex!(::Tuple{Int64,Int64,Int64}, ::Int64, ::Int64)
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catch e
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println(e)
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end
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# 大多数组的函数同样支持元组
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length(tup) # => 3
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tup[1:2] # => (1,2)
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in(2, tup) # => true
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# 可以将元组的元素解包赋给变量
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a, b, c = (1, 2, 3) # => (1,2,3)
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a # => 1
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b # => 2
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c # => 3
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# 不用括号也可以
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d, e, f = 4, 5, 6 # => (4,5,6)
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d # => 4
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e # => 5
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f # => 6
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# 单元素 tuple 不等于其元素值
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(1,) == 1 # => false
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(1) == 1 # => true
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# 交换值
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e, d = d, e # => (5,4)
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d # => 5
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e # => 4
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# 字典用于储存映射(mappings)（键值对）
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empty_dict = Dict() # => Dict{Any,Any} with 0 entries
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# 也可以用字面量创建字典
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filled_dict = Dict("one" => 1, "two" => 2, "three" => 3)
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# => Dict{String,Int64} with 3 entries:
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# => "two" => 2, "one" => 1, "three" => 3
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# 用 [] 获得键值
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filled_dict["one"] # => 1
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# 获得所有键
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keys(filled_dict)
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# => Base.KeySet for a Dict{String,Int64} with 3 entries. Keys:
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# => "two", "one", "three"
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# 注意，键的顺序不是插入时的顺序
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# 获得所有值
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values(filled_dict)
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# => Base.ValueIterator for a Dict{String,Int64} with 3 entries. Values:
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# => 2, 1, 3
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# 注意，值的顺序也一样
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# 用 in 检查键值是否已存在，用 haskey 检查键是否存在
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in(("one" => 1), filled_dict) # => true
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in(("two" => 3), filled_dict) # => false
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haskey(filled_dict, "one") # => true
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haskey(filled_dict, 1) # => false
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# 获取不存在的键的值会抛出异常
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try
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filled_dict["four"] # => ERROR: KeyError: key "four" not found
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catch e
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println(e)
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end
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# 使用 get 可以提供默认值来避免异常
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# get(dictionary,key,default_value)
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get(filled_dict, "one", 4) # => 1
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get(filled_dict, "four", 4) # => 4
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# Set 表示无序不可重复的值的集合
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empty_set = Set() # => Set(Any[])
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# 初始化一个带初值的 Set
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filled_set = Set([1, 2, 2, 3, 4]) # => Set([4, 2, 3, 1])
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# 新增值
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push!(filled_set, 5) # => Set([4, 2, 3, 5, 1])
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# 检查 Set 中是否存在某值
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in(2, filled_set) # => true
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in(10, filled_set) # => false
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# 交集，并集，差集
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other_set = Set([3, 4, 5, 6]) # => Set([4, 3, 5, 6])
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intersect(filled_set, other_set) # => Set([4, 3, 5])
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union(filled_set, other_set) # => Set([4, 2, 3, 5, 6, 1])
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setdiff(Set([1,2,3,4]), Set([2,3,5])) # => Set([4, 1])
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####################################################
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## 3. 控制语句
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####################################################
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# 声明一个变量
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some_var = 5
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# 这是一个 if 语句块，其中的缩进不是必须的
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if some_var > 10
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println("some_var is totally bigger than 10.")
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elseif some_var < 10 # elseif 是可选的
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println("some_var is smaller than 10.")
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else # else 也是可选的
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println("some_var is indeed 10.")
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end
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# => some_var is smaller than 10.
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# For 循环遍历
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# 可迭代的类型包括：Range, Array, Set, Dict 和 AbstractString
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for animal = ["dog", "cat", "mouse"]
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println("$animal is a mammal")
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# 你可以用 $ 将变量或表达式插入字符串中
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end
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# => dog is a mammal
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# => cat is a mammal
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# => mouse is a mammal
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# 你也可以不用「=」而使用「in」
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for animal in ["dog", "cat", "mouse"]
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println("$animal is a mammal")
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end
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# => dog is a mammal
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# => cat is a mammal
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# => mouse is a mammal
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for pair in Dict("dog" => "mammal", "cat" => "mammal", "mouse" => "mammal")
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from, to = pair
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println("$from is a $to")
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end
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# => mouse is a mammal
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# => cat is a mammal
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# => dog is a mammal
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# 注意！这里的输出顺序和上面的不同
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for (k, v) in Dict("dog" => "mammal", "cat" => "mammal", "mouse" => "mammal")
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println("$k is a $v")
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end
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# => mouse is a mammal
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# => cat is a mammal
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# => dog is a mammal
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# While 循环
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let x = 0
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while x < 4
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println(x)
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x += 1 # x = x + 1 的缩写
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end
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end
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# => 0
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# => 1
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# => 2
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# => 3
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# 用 try/catch 处理异常
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try
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error("help")
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catch e
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println("caught it $e")
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end
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# => caught it ErrorException("help")
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####################################################
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## 4. 函数
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####################################################
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||
# 关键字 function 用于定义函数
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# function name(arglist)
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# body...
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# end
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function add(x, y)
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println("x is $x and y is $y")
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# 函数会返回最后一行的值
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x + y
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end
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add(5, 6)
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# => x is 5 and y is 6
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# => 11
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# 更紧凑的定义函数
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f_add(x, y) = x + y # => f_add (generic function with 1 method)
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f_add(3, 4) # => 7
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# 函数可以将多个值作为元组返回
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fn(x, y) = x + y, x - y # => fn (generic function with 1 method)
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fn(3, 4) # => (7, -1)
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# 还可以定义接收可变长参数的函数
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function varargs(args...)
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return args
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# 使用 return 可以在函数内的任何地方返回
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end
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# => varargs (generic function with 1 method)
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varargs(1,2,3) # => (1,2,3)
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# 省略号「...」称为 splat
|
||
# 刚刚用在了函数定义中
|
||
# 在调用函数时也可以使用它，此时它会把数组或元组解包为参数列表
|
||
add([5,6]...) # 等价于 add(5,6)
|
||
|
||
x = (5, 6) # => (5,6)
|
||
add(x...) # 等价于 add(5,6)
|
||
|
||
# 可定义带可选参数的函数
|
||
function defaults(a, b, x=5, y=6)
|
||
return "$a $b and $x $y"
|
||
end
|
||
# => defaults (generic function with 3 methods)
|
||
|
||
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: MethodError: no method matching defaults(::Char)
|
||
defaults() # => ERROR: MethodError: no method matching defaults()
|
||
catch e
|
||
println(e)
|
||
end
|
||
|
||
# 还可以定义带关键字参数的函数
|
||
function keyword_args(;k1=4, name2="hello") # 注意分号 ';'
|
||
return Dict("k1" => k1, "name2" => name2)
|
||
end
|
||
# => keyword_args (generic function with 1 method)
|
||
|
||
keyword_args(name2="ness") # => ["name2"=>"ness", "k1"=>4]
|
||
keyword_args(k1="mine") # => ["name2"=>"hello", "k1"=>"mine"]
|
||
keyword_args() # => ["name2"=>"hello", "k1"=>4]
|
||
|
||
# 可以在一个函数中组合各种类型的参数
|
||
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 (generic function with 2 methods)
|
||
|
||
all_the_args(1, 3, keyword_arg=4)
|
||
# => 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
|
||
# => create_adder (generic function with 1 method)
|
||
|
||
# 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 是等价的
|
||
function create_adder(x)
|
||
y -> x + y
|
||
end
|
||
# => create_adder (generic function with 1 method)
|
||
|
||
# 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
|
||
# => create_adder (generic function with 1 method)
|
||
|
||
add_10 = create_adder(10) # => (::getfield(Main, Symbol("#adder#11")){Int64})
|
||
# (generic function with 1 method)
|
||
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 让 map 更美观
|
||
[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
|
||
|
||
# 类型可用于文档化代码、执行优化以及多重派分(dispatch)
|
||
# Julia 并不只是静态的检查类型
|
||
|
||
# 用户还可以自定义类型
|
||
# 就跟其它语言的 record 或 struct 一样
|
||
# 用 `struct` 关键字定义新的类型
|
||
|
||
# struct Name
|
||
# field::OptionalType
|
||
# ...
|
||
# end
|
||
struct Tiger
|
||
taillength::Float64
|
||
coatcolor # 不带类型标注相当于 `::Any`
|
||
end
|
||
|
||
# 默认构造函数的参数是类型的属性，按类型定义中的顺序排列
|
||
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")
|
||
|
||
# 类似 struct 的类型被称为具体类型
|
||
# 它们可被实例化，但不能有子类型
|
||
# 另一种类型是抽象类型
|
||
|
||
# 抽象类型名
|
||
abstract type Cat end # 仅仅是指向类型结构层次的一个名称
|
||
|
||
# 抽象类型不能被实例化，但可以有子类型
|
||
# 例如，Number 就是抽象类型
|
||
subtypes(Number) # => 2-element Array{Any,1}:
|
||
# => Complex
|
||
# => Real
|
||
subtypes(Cat) # => 0-element Array{Any,1}
|
||
|
||
# AbstractString，类如其名，也是一个抽象类型
|
||
subtypes(AbstractString) # => 4-element Array{Any,1}:
|
||
# => String
|
||
# => SubString
|
||
# => SubstitutionString
|
||
# => Test.GenericString
|
||
|
||
# 所有的类型都有父类型。可以用函数 `supertype` 得到父类型
|
||
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
|
||
# 除了 Int64 外，其余的类型都是抽象类型
|
||
typeof("fire") # => String
|
||
supertype(String) # => AbstractString
|
||
supertype(AbstractString) # => Any
|
||
supertype(SubString) # => AbstractString
|
||
|
||
# <: 是子类型化操作符
|
||
struct Lion <: Cat # Lion 是 Cat 的子类型
|
||
mane_color
|
||
roar::AbstractString
|
||
end
|
||
|
||
# 可以继续为你的类型定义构造函数
|
||
# 只需要定义一个与类型同名的函数，并调用已有的构造函数得到正确的类型
|
||
Lion(roar::AbstractString) = Lion("green", roar) # => Lion
|
||
# 这是一个外部构造函数，因为它在类型定义之外
|
||
|
||
struct 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
|
||
# 像 Panther 一样使用内置构造函数，让你可以控制如何构建类型的值
|
||
# 应该尽量使用外部构造函数，而不是内部构造函数
|
||
|
||
####################################################
|
||
## 6. 多分派
|
||
####################################################
|
||
|
||
# Julia 中所有的函数都是通用函数，或者叫做泛型函数(generic functions)
|
||
# 也就是说这些函数都是由许多小方法组合而成的
|
||
# Lion 的每一种构造函数都是通用函数 Lion 的一个方法
|
||
|
||
# 我们来看一个非构造函数的例子
|
||
# 首先，让我们定义一个函数 meow
|
||
|
||
# Lion, Panther, Tiger 的 meow 定义分别为
|
||
function meow(animal::Lion)
|
||
animal.roar # 使用点记号「.」访问属性
|
||
end
|
||
# => meow (generic function with 1 method)
|
||
|
||
function meow(animal::Panther)
|
||
"grrr"
|
||
end
|
||
# => meow (generic function with 2 methods)
|
||
|
||
function meow(animal::Tiger)
|
||
"rawwwr"
|
||
end
|
||
# => meow (generic function with 3 methods)
|
||
|
||
# 试试 meow 函数
|
||
meow(tigger) # => "rawwwr"
|
||
meow(Lion("brown", "ROAAR")) # => "ROAAR"
|
||
meow(Panther()) # => "grrr"
|
||
|
||
# 回顾类型的层次结构
|
||
Tiger <: Cat # => false
|
||
Lion <: Cat # => true
|
||
Panther <: Cat # => true
|
||
|
||
# 定义一个接收 Cat 类型的函数
|
||
function pet_cat(cat::Cat)
|
||
println("The cat says $(meow(cat))")
|
||
end
|
||
# => pet_cat (generic function with 1 method)
|
||
|
||
pet_cat(Lion("42")) # => The cat says 42
|
||
try
|
||
pet_cat(tigger) # => ERROR: MethodError: no method matching pet_cat(::Tiger)
|
||
catch e
|
||
println(e)
|
||
end
|
||
|
||
# 在面向对象语言中，通常都是单分派
|
||
# 这意味着使用的方法取决于第一个参数的类型
|
||
# 而 Julia 中选择方法时会考虑到所有参数的类型
|
||
|
||
# 让我们定义一个有更多参数的函数，这样我们就能看出区别
|
||
function fight(t::Tiger, c::Cat)
|
||
println("The $(t.coatcolor) tiger wins!")
|
||
end
|
||
# => fight (generic function with 1 method)
|
||
|
||
fight(tigger, Panther()) # => The orange tiger wins!
|
||
fight(tigger, Lion("ROAR")) # => fight(tigger, Lion("ROAR"))
|
||
|
||
# 让我们修改一下传入 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()) # => The orange tiger wins!
|
||
fight(tigger, Lion("ROAR")) # => The green-maned lion wins!
|
||
|
||
# 我们不需要一只老虎参与战斗
|
||
fight(l::Lion, c::Cat) = println("The victorious cat says $(meow(c))")
|
||
# => fight (generic function with 3 methods)
|
||
|
||
fight(Lion("balooga!"), Panther()) # => The victorious cat says grrr
|
||
try
|
||
fight(Panther(), Lion("RAWR"))
|
||
# => ERROR: MethodError: no method matching fight(::Panther, ::Lion)
|
||
# => Closest candidates are:
|
||
# => fight(::Tiger, ::Lion) at ...
|
||
# => fight(::Tiger, ::Cat) at ...
|
||
# => fight(::Lion, ::Cat) at ...
|
||
# => ...
|
||
catch e
|
||
println(e)
|
||
end
|
||
|
||
# 试试把 Cat 放在前面
|
||
fight(c::Cat, l::Lion) = println("The cat beats the Lion")
|
||
# => fight (generic function with 4 methods)
|
||
|
||
# 由于无法判断该使用哪个 fight 方法，而产生了错误
|
||
try
|
||
fight(Lion("RAR"), Lion("brown", "rarrr"))
|
||
# => ERROR: MethodError: fight(::Lion, ::Lion) is ambiguous. Candidates:
|
||
# => fight(c::Cat, l::Lion) in Main at ...
|
||
# => fight(l::Lion, c::Cat) in Main at ...
|
||
# => Possible fix, define
|
||
# => fight(::Lion, ::Lion)
|
||
# => ...
|
||
catch e
|
||
println(e)
|
||
end
|
||
# 在不同版本的 Julia 中错误信息可能有所不同
|
||
|
||
fight(l::Lion, l2::Lion) = println("The lions come to a tie")
|
||
# => fight (generic function with 5 methods)
|
||
fight(Lion("RAR"), Lion("brown", "rarrr")) # => The lions come to a tie
|
||
|
||
|
||
# 深入编译器之后
|
||
# 你还可以看看 llvm 以及它生成的汇编代码
|
||
|
||
square_area(l) = l * l # => square_area (generic function with 1 method)
|
||
square_area(5) # => 25
|
||
|
||
# 当我们喂给 square_area 一个整数时会发生什么？
|
||
code_native(square_area, (Int32,), syntax = :intel)
|
||
# .text
|
||
# ; Function square_area {
|
||
# ; Location: REPL[116]:1 # 函数序言 (Prologue)
|
||
# push rbp
|
||
# mov rbp, rsp
|
||
# ; Function *; {
|
||
# ; Location: int.jl:54
|
||
# imul ecx, ecx # 求 l 的平方，并把结果放在 ECX 中
|
||
# ;}
|
||
# mov eax, ecx
|
||
# pop rbp # 还原旧的基址指针(base pointer)
|
||
# ret # 返回值放在 EAX 中
|
||
# nop dword ptr [rax + rax]
|
||
# ;}
|
||
# 使用 syntax 参数指定输出语法。默认为 AT&T 格式，这里指定为 Intel 格式
|
||
|
||
code_native(square_area, (Float32,), syntax = :intel)
|
||
# .text
|
||
# ; Function square_area {
|
||
# ; Location: REPL[116]:1
|
||
# push rbp
|
||
# mov rbp, rsp
|
||
# ; Function *; {
|
||
# ; Location: float.jl:398
|
||
# vmulss xmm0, xmm0, xmm0 # 标量双精度乘法 (AVX)
|
||
# ;}
|
||
# pop rbp
|
||
# ret
|
||
# nop word ptr [rax + rax]
|
||
# ;}
|
||
|
||
code_native(square_area, (Float64,), syntax = :intel)
|
||
# .text
|
||
# ; Function square_area {
|
||
# ; Location: REPL[116]:1
|
||
# push rbp
|
||
# mov rbp, rsp
|
||
# ; Function *; {
|
||
# ; Location: float.jl:399
|
||
# vmulsd xmm0, xmm0, xmm0 # 标量双精度乘法 (AVX)
|
||
# ;}
|
||
# pop rbp
|
||
# ret
|
||
# nop word ptr [rax + rax]
|
||
# ;}
|
||
|
||
# 注意！只要参数中有浮点数，Julia 就会使用浮点指令
|
||
# 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,), syntax = :intel)
|
||
# .text
|
||
# ; Function circle_area {
|
||
# ; Location: REPL[121]:1
|
||
# push rbp
|
||
# mov rbp, rsp
|
||
# ; Function *; {
|
||
# ; Location: operators.jl:502
|
||
# ; Function *; {
|
||
# ; Location: promotion.jl:314
|
||
# ; Function promote; {
|
||
# ; Location: promotion.jl:284
|
||
# ; Function _promote; {
|
||
# ; Location: promotion.jl:261
|
||
# ; Function convert; {
|
||
# ; Location: number.jl:7
|
||
# ; Function Type; {
|
||
# ; Location: float.jl:60
|
||
# vcvtsi2sd xmm0, xmm0, ecx # 从内存中读取整数 r
|
||
# movabs rax, 497710928 # 读取 pi
|
||
# ;}}}}}
|
||
# ; Function *; {
|
||
# ; Location: float.jl:399
|
||
# vmulsd xmm1, xmm0, qword ptr [rax] # pi * r
|
||
# vmulsd xmm0, xmm1, xmm0 # (pi * r) * r
|
||
# ;}}
|
||
# pop rbp
|
||
# ret
|
||
# nop dword ptr [rax]
|
||
# ;}
|
||
|
||
code_native(circle_area, (Float64,), syntax = :intel)
|
||
# .text
|
||
# ; Function circle_area {
|
||
# ; Location: REPL[121]:1
|
||
# push rbp
|
||
# mov rbp, rsp
|
||
# movabs rax, 497711048
|
||
# ; Function *; {
|
||
# ; Location: operators.jl:502
|
||
# ; Function *; {
|
||
# ; Location: promotion.jl:314
|
||
# ; Function *; {
|
||
# ; Location: float.jl:399
|
||
# vmulsd xmm1, xmm0, qword ptr [rax]
|
||
# ;}}}
|
||
# ; Function *; {
|
||
# ; Location: float.jl:399
|
||
# vmulsd xmm0, xmm1, xmm0
|
||
# ;}
|
||
# pop rbp
|
||
# ret
|
||
# nop dword ptr [rax + rax]
|
||
# ;}
|
||
```
|
||
|
||
## 拓展阅读材料
|
||
|
||
你可以在 [Julia 中文文档](http://docs.juliacn.com/latest/) / [Julia 文档(en)](https://docs.julialang.org/)
|
||
中获得关于 Julia 的更多细节。
|
||
|
||
如果有任何问题可以去 [Julia 中文社区](http://discourse.juliacn.com/) / [官方社区(en)](https://discourse.julialang.org/) 提问，大家对待新手都非常的友好。
|