--- language: Julia filename: learn-julia-zh.jl contributors: - ["Jichao Ouyang", "http://oyanglul.us"] translators: - ["Jichao Ouyang", "http://oyanglul.us"] - ["woclass", "https://github.com/inkydragon"] lang: zh-cn --- ```julia # 单行注释只需要一个井号 #= 多行注释 只需要以 '#=' 开始 '=#' 结束 还可以嵌套. =# #################################################### ## 1. 原始类型与操作符 #################################################### # Julia 中一切皆为表达式 # 这是一些基本数字类型 typeof(3) # => Int64 typeof(3.2) # => Float64 typeof(2 + 1im) # => Complex{Int64} typeof(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 10 / 2 # => 5.0 # 整数除法总是返回浮点数 div(5, 2) # => 2 # 使用 div 可以获得整除的结果 5 \ 35 # => 7.0 2^2 # => 4 # 幂运算，不是异或 (xor) 12 % 10 # => 2 # 用括号提高优先级 (1 + 3) * 2 # => 8 # 位操作符 ~2 # => -3 # 按位非 (not) 3 & 5 # => 1 # 按位与 (and) 2 | 4 # => 6 # 按位或 (or) xor(2, 4) # => 6 # 按位异或 (xor) 2 >>> 1 # => 1 # 逻辑右移 2 >> 1 # => 1 # 算术右移 2 << 1 # => 4 # 逻辑/算术左移 # 可以用函数 bitstring 查看二进制数。 bitstring(12345) # => "0000000000000000000000000000000000000000000000000011000000111001" bitstring(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 # 链式比较 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 ascii("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。 # 另一种输出格式化字符串的方法是使用标准库 Printf 中的 Printf 宏 using Printf @printf "%d is less than %f\n" 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!") # 字符串可以按字典序进行比较 "good" > "bye" # => true "good" == "good" # => true "1 + 2 = 3" == "1 + 2 = $(1 + 2)" # => true #################################################### ## 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: UndefVarError: some_other_var not defined catch e println(e) end # 变量名必须以下划线或字母开头 # 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 Array{Int64,1} # 一维数组可以以逗号分隔值的方式声明 b = [4, 5, 6] # => 3-element Array{Int64,1}: [4, 5, 6] b = [4; 5; 6] # => 3-element Array{Int64,1}: [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] # => 2×2 Array{Int64,2}: [1 2; 3 4] # 指定数组的类型 b = Int8[4, 5, 6] # => 3-element Array{Int8,1}: [4, 5, 6] # 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 弹出尾部的元素 pop!(b) # => 6 b # => [4,5] # 再放回去 push!(b, 6) # => [4,5,6] b # => [4,5,6] a[1] # => 1 # 永远记住 Julia 的引索从 1 开始！而不是 0！ # 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 # 数组还支持 popfirst! 和 pushfirst! popfirst!(a) # => 1 a # => [2,4,3,4,5,6] pushfirst!(a, 7) # => [7,2,4,3,4,5,6] a # => [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] # => 3-element Array{Int64,1}: [5,4,6] sort(arr) # => [4,5,6] arr # => [5,4,6] sort!(arr) # => [4,5,6] arr # => [4,5,6] # 数组越界会抛出 BoundsError try a[0] # => ERROR: BoundsError: attempt to access 7-element Array{Int64,1} at # index [0] # => Stacktrace: # => [1] getindex(::Array{Int64,1}, ::Int64) at .\array.jl:731 # => [2] top-level scope at none:0 # => [3] ... # => in expression starting at ...\LearnJulia.jl:188 a[end + 1] # => ERROR: BoundsError: attempt to access 7-element Array{Int64,1} at # index [8] # => Stacktrace: # => [1] getindex(::Array{Int64,1}, ::Int64) at .\array.jl:731 # => [2] top-level scope at none:0 # => [3] ... # => in expression starting at ...\LearnJulia.jl:196 catch e println(e) end # 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 # 你可以在 Julia 安装目录下的 share/julia 文件夹里找到这些标准库 # 可以用 range 初始化数组 a = [1:5;] # => 5-element Array{Int64,1}: [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 # => [3,5] # 用 append! 连接数组 b = [1,2,3] append!(a, b) # => [1, 2, 3, 4, 5, 1, 2, 3] a # => [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 # 元组(Tuples)是不可变的 tup = (1, 2, 3) # => (1,2,3) typeof(tup) # => Tuple{Int64,Int64,Int64} tup[1] # => 1 try tup[1] = 3 # => ERROR: MethodError: no method matching # setindex!(::Tuple{Int64,Int64,Int64}, ::Int64, ::Int64) catch e println(e) end # 大多数组的函数同样支持元组 length(tup) # => 3 tup[1:2] # => (1,2) in(2, tup) # => true # 可以将元组的元素解包赋给变量 a, b, c = (1, 2, 3) # => (1,2,3) a # => 1 b # => 2 c # => 3 # 不用括号也可以 d, e, f = 4, 5, 6 # => (4,5,6) d # => 4 e # => 5 f # => 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 # => 5 e # => 4 # 字典Dictionaries store mappings empty_dict = Dict() # => Dict{Any,Any} with 0 entries # 也可以用字面量创建字典 filled_dict = Dict("one" => 1, "two" => 2, "three" => 3) # => Dict{String,Int64} with 3 entries: # => "two" => 2, "one" => 1, "three" => 3 # 用 [] 获得键值 filled_dict["one"] # => 1 # 获得所有键 keys(filled_dict) # => Base.KeySet for a Dict{String,Int64} with 3 entries. Keys: # => "two", "one", "three" # 注意，键的顺序不是插入时的顺序 # 获得所有值 values(filled_dict) # => Base.ValueIterator for a Dict{String,Int64} with 3 entries. Values: # => 2, 1, 3 # 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: KeyError: key "four" not found 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 # Sets 表示无序不可重复的值的集合 empty_set = Set() # => Set(Any[]) # 初始化一个带初值的 Set filled_set = Set([1, 2, 2, 3, 4]) # => Set([4, 2, 3, 1]) # 新增值 push!(filled_set, 5) # => Set([4, 2, 3, 5, 1]) # 检查 Set 中是否存在某值 in(2, filled_set) # => true in(10, filled_set) # => false # 交集，并集，差集 other_set = Set([3, 4, 5, 6]) # => Set([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]) #################################################### ## 3. 控制语句 #################################################### # 声明一个变量 some_var = 5 # 这是一个 if 语句块，其中的缩进不是必须的 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 # => some_var is smaller than 10. # For 循环遍历 # 可迭代的类型包括：Range, Array, Set, Dict 和 AbstractString for animal = ["dog", "cat", "mouse"] println("$animal is a mammal") # 你可以用 $ 将变量或表达式插入字符串中 end # => dog is a mammal # => cat is a mammal # => mouse is a mammal # 你也可以不用 '=' 而使用 'in' for animal in ["dog", "cat", "mouse"] println("$animal is a mammal") end # => dog is a mammal # => cat is a mammal # => mouse is a mammal for pair in Dict("dog" => "mammal", "cat" => "mammal", "mouse" => "mammal") from, to = pair println("$from is a $to") end # => mouse is a mammal # => cat is a mammal # => dog is a mammal # 注意！这里的输出顺序和上面的不同 for (k, v) in Dict("dog" => "mammal", "cat" => "mammal", "mouse" => "mammal") println("$k is a $v") end # => mouse is a mammal # => cat is a mammal # => dog is a mammal # While 循环 let x = 0 while x < 4 println(x) x += 1 # x = x + 1 的缩写 end end # => 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 # ```