From: dblack@...
Date: 2007-01-28T13:08:50+09:00
Subject: Re: pass by reference?

Hi --

On Sun, 28 Jan 2007, Thomas Hafner wrote:

> Xavier Noria <fxn@hashref.com> wrote/schrieb <73286BF0-AFE1-40C1-9704-16A3E129CD56@hashref.com>:
>
>> In C++ since the copy constructor is involved, I found people in
>> freenode#c++ consider &-arguments to be pass-by-reference because
>> they can modify the objects in the caller, albeit the assigment test
>> discussed in the thread does not work, that'd be
>>
>>    def m(b)
>>      b = 7
>>    end
>>
>>    a = 3
>>    m(a)
>>    # a expected to be 7 in pass-by-reference
>
> That's another story. With the code above you rather reset b to a new
> object instead of modifying the passed object. Look here:
>
> def m(b)
>  b.shift
>  b.unshift(7)
> end
> a = [3]
> m(a)
> => [7]
>
> Would that be the same with pass-by-value? No, I don't think so.

It depends what value you're passing.  If the value is an array, and
it gets copied into b, then it wouldn't work that way; but what's
happening is that a *reference* to an array is getting passed by
value.  That value (which is a reference to an array) is assigned to
the variable a in the caller's scope, and also to the variable b
inside the method.


David

-- 
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