引用的 Julia 函数参数 [英] Julia function argument by reference

问题描述

文档说

在 Julia 中，函数的所有参数都通过引用传递.

In Julia, all arguments to functions are passed by reference.

所以我很惊讶地发现这两个函数的行为有所不同:

so I was quite surprised to see a difference in the behaviour of these two functions:

function foo!(r::Array{Int64})                                                                                                                                                                                     
        r=r+1                                                                                                                                                                                                      
end


function foobar!(r::Array{Int64})                                                                                                                                                                                  
        for i=1:length(r)                                                                                                                                                                                          
                r[i]=r[i]+1                                                                                                                                                                                        
        end                                                                                                                                                                                                        
end 

这是出乎意料的不同输出:

here is the unexpectedly different output:

julia> myarray
2-element Array{Int64,1}:
 0
 0

julia> foo!(myarray);

julia> myarray
2-element Array{Int64,1}:
 0
 0

julia> foobar!(myarray);

julia> myarray
2-element Array{Int64,1}:
 1
 1

如果数组是通过引用传递的，我会期待 foo!将零更改为一.

if the array is passed by reference, I would have expected foo! to change the zeros to ones.

推荐答案

r=r+1 是一个 Assignment 语句，这意味着它重新分配了 r，因此它不再引用它在父作用域中的对.但是 r[i]=r[i]+1 变异 r 值，变异不同于赋值(这里有一个很好的描述)，之后 r 仍然引用它在父作用域中的 pair 变量.

r=r+1 is an Assignment statement, this means it reallocates r, so it no longer refers to its pair in the parent scope. but r[i]=r[i]+1 Mutates r value, mutation is differ from assignment (a good description here), and after that r still refers to its pair variable in the parent scope.

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