http://d.puremagic.com/issues/show_bug.cgi?id=10638

           Summary: Assignment can't be used as a condition
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: freeslave93@gmail.com


--- Comment #0 from Roman <freeslave93@gmail.com> 2013-07-14 04:44:07 PDT ---
Suppose code

void main()
{
    int i = 0;
    if (i = 1)
    {
        //......
    }
}

dmd compiler generates error: "assignment cannot be used as a condition, perhaps == was meant?"

But next code passed successfully:

void main()
{
    if (int i = 1)
    {
        //......
    }
}

It's a bit odd that assignment can not be used as condition while declaration can be.

It works fine if we replace first code snippet with this:

void main()
{
    int i = 0;
    if (cast(bool)(i = 1))
    {
        //......
    }
}

I guess assignment has no implicit cast to bool, it's weird too. If it's not error, please, explain me the reasons of this restriction.

Also dlang.org defines ifStatement as "if ( IfCondition ) ThenStatement", where
ifCondition can be Expression (hence AssignExpression too), but it seems it
does not work at practice.

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9999 <mailnew4ster@gmail.com> changed:

           What    |Removed                     |Added
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--- Comment #1 from 9999 <mailnew4ster@gmail.com> 2013-07-14 04:48:30 PDT ---
I believe the primary reason is to prevent bugs where == was meant and not =. Usually, what you want to do is:

void main()
{
    int i = f();
    if (i == 1)
    {
        //......
    }
}

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bearophile_hugs@eml.cc changed:

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--- Comment #2 from bearophile_hugs@eml.cc 2013-07-14 04:58:13 PDT ---
(In reply to comment #1)

> I believe the primary reason is to prevent bugs where == was meant and not =. Usually, what you want to do is:
> 
> void main()
> {
>     int i = f();
>     if (i == 1)
>     {
>         //......
>     }
> }

Right. D is working as designed here, it helps avoid bugs.



> Also dlang.org defines ifStatement as "if ( IfCondition ) ThenStatement",
> where ifCondition can be Expression (hence AssignExpression too),
> but it seems it does not work at practice.

Then maybe that's what needs fixing.

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