[Issue 2418] Same-value string (char[]) literals get overwritten (unlike array literals)

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=2418


2korden at gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |RESOLVED
         Resolution|                            |INVALID




------- Comment #4 from 2korden at gmail.com  2008-10-15 00:02 -------
> ------- Comment #3 from business3 at twistedpairgaming.com  2008-10-14  
>
> I don't think that's applicable (or at least, it shouldn't be). Here's a
> shortened example:
>
> char[] a = "AAA";
> a[0] = '!';
> char[] b = "AAA";
>
> It's absurd that 'b' should become "!AA".
Well, that's what I expect, at least :)

> It's clear that the compiler is
> "optimizing" both "AAA" string literals into the same reference:
>
> char[] _tmp1 = "AAA";
> char[] a = _tmp1;
> a[0] = '!';
> char[] b = _tmp1;

Of course it does! This string literal is put into executable. "AAA" is just a
pointer to it.

Please, understand that char[] is nothing more than a pointer to a string and
an associated length. When you change the string via pointer, everyone who has
that pointer gets the change. Compare to object:

class A
{
    int i = 15;
}

A aaa = new A(); // aaa is an analog of "AAA"
A a = aaa;
writefln(a); // prints 15
a.i = 42;

A b = aaa;
writefln(b); // why the hell it prints 42????

This is because you don't make a copy of aaa.

Here is another example:

while (true) {
    char[] a = "AAA";
    a[0] = '!';   // in the next iteration, should a be "AAA" again?
}

If answer is yes, then there should be a memory allocation in line 2 under the
hood. You can't get new string every time without a memory allocation. This,
however, definitely should not occur. If you want to make an allocation - do it
yourself explicitely.

Code with the behaviour you expect should be as follows:
while (true) {
    char[] a = "AAA".dup;
    writefln(a);
    a[0] = '!';
    writefln(a);
}

This is by design, it works as it should. It can't be 'fixed' because it is not
broken.

> Besides, at the very least there's still an inconsistency:
>
> char[] a = "AAA";
> a[0] = '!';
> char[] b = "AAA";  // b is "!AA"
>
> char[] c = ['A', 'A', 'A'];
> c[0] = '!';
> char[] d = ['A', 'A', 'A'];  // d is "AAA"

I agree, this might be a bug, d really ought to be "!AAA"!
Do you want to create a new bugreport so that the latter case would be 'fixed'?
:)


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