It looks like the rt is not calling the postblit constructor when concatenating arrays. For example, the following code:

import std.stdio;

struct Test
{
   this(this) { writeln("copy done"); }
   void opAssign(Test rhs) { writeln("assignment done"); }
   ~this() { writeln("destructor called"); }
}

void main()
{
   Test[] tests = new Test[1];
   {
      Test test;
      tests ~= test;
   }
   writeln("done");
}

Gives the following output:

destructor called
done

The dtr for 'Test test;' is getting call after the scope exits but the postblit ctr for 'tests[0]' is never called. I believe the output of this code should either be:

done

or:

copy done
destructor called
done

Thanks!
-Jose

On Fri, 17 Jun 2011 00:05:56 -0400, Jose Armando Garcia <jsancio@gmail.com> wrote:

> It looks like the rt is not calling the postblit constructor when
> concatenating arrays. For example, the following code:
>
> import std.stdio;
>
> struct Test
> {
>    this(this) { writeln("copy done"); }
>    void opAssign(Test rhs) { writeln("assignment done"); }
>    ~this() { writeln("destructor called"); }
> }
>
> void main()
> {
>    Test[] tests = new Test[1];
>    {
>       Test test;
>       tests ~= test;
>    }
>    writeln("done");
> }
>
> Gives the following output:
>
> destructor called
> done
>
> The dtr for 'Test test;' is getting call after the scope exits but the
> postblit ctr for 'tests[0]' is never called. I believe the output of
> this code should either be:
>
> done
>
> or:
>
> copy done
> destructor called
> done
>

You are right, postblit should be called.  http://d.puremagic.com/issues/show_bug.cgi?id=5272

I'll look at doing a fix.

-Steve

On Fri, 17 Jun 2011 06:42:51 -0400, Steven Schveighoffer <schveiguy@yahoo.com> wrote:

> On Fri, 17 Jun 2011 00:05:56 -0400, Jose Armando Garcia <jsancio@gmail.com> wrote:
>
>> It looks like the rt is not calling the postblit constructor when
>> concatenating arrays. For example, the following code:
>>
>> import std.stdio;
>>
>> struct Test
>> {
>>    this(this) { writeln("copy done"); }
>>    void opAssign(Test rhs) { writeln("assignment done"); }
>>    ~this() { writeln("destructor called"); }
>> }
>>
>> void main()
>> {
>>    Test[] tests = new Test[1];
>>    {
>>       Test test;
>>       tests ~= test;
>>    }
>>    writeln("done");
>> }
>>
>> Gives the following output:
>>
>> destructor called
>> done
>>
>> The dtr for 'Test test;' is getting call after the scope exits but the
>> postblit ctr for 'tests[0]' is never called. I believe the output of
>> this code should either be:
>>
>> done
>>
>> or:
>>
>> copy done
>> destructor called
>> done
>>
>
> You are right, postblit should be called.  http://d.puremagic.com/issues/show_bug.cgi?id=5272
>
> I'll look at doing a fix.

https://github.com/D-Programming-Language/druntime/pull/29

See if that helps.  On my system, your code now results in your expected output.

-Steve

Steven Schveighoffer wrote:
> https://github.com/D-Programming-Language/druntime/pull/29
>
> See if that helps.  On my system, your code now results in your expected output.
>
> -Steve

If the compiler optimizes well enough the output given could be valid (it might construct the struct directly where it belongs). This needs some investigation. Anyways, is druntime the correct place to fix this? If it _is_ a bug, isn't it a compiler bug and not a bug in druntime? After a quick glimpse over your patch I think the output will never be just "done" now.


Timon

On Fri, 17 Jun 2011 18:52:05 -0400, Timon Gehr <timon.gehr@gmx.ch> wrote:

> Steven Schveighoffer wrote:
>> https://github.com/D-Programming-Language/druntime/pull/29
>>
>> See if that helps.  On my system, your code now results in your expected
>> output.
>>
>> -Steve
>
> If the compiler optimizes well enough the output given could be valid (it might
> construct the struct directly where it belongs). This needs some investigation.
> Anyways, is druntime the correct place to fix this? If it _is_ a bug, isn't it a
> compiler bug and not a bug in druntime? After a quick glimpse over your patch I
> think the output will never be just "done" now.

The patch is still necessary in cases where the value being appended is not a temporary.  For example, if in the OP's code the test variable was used after appending it to the array.

Michel Fortin also brought up the point in a comment on the pull request.  But the reality is, druntime cannot do any better without help from the compiler (the runtime needs to be told when to refrain from running a postblit).  It's a separate bug.

However, I think there is nothing invalid with doing both the postblit and the destructor on the temporary.  So at least the code is correctly calling the postblit.

-Steve