http://d.puremagic.com/issues/show_bug.cgi?id=8634

           Summary: Anonymous function parameters
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: maxim@maxim-fomin.ru


--- Comment #0 from Maxim Fomin <maxim@maxim-fomin.ru> 2012-09-09 05:28:51 PDT ---
void foo(int)
{

}

void main()
{
    foo(5);
}

Although anonymous function parameters may be used in function declarations, it seems that dmd doesn't check whether a function declaration is a definition too.

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http://d.puremagic.com/issues/show_bug.cgi?id=8634


bearophile_hugs@eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bearophile_hugs@eml.cc


--- Comment #1 from bearophile_hugs@eml.cc 2012-09-09 06:53:14 PDT ---
(In reply to comment #0)
> void foo(int)
> {
> 
> }
> 
> void main()
> {
>     foo(5);
> }
> 
> Although anonymous function parameters may be used in function declarations, it seems that dmd doesn't check whether a function declaration is a definition too.

What's the problem here?

foo() not giving a name to its first argument means the programmer is stating
foo() never uses its first argument, and the D language allows the programmer
to enforce this desire.

This feature also allows to avoid "unused argument warnings" once/where such warning is available.

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--- Comment #2 from Maxim Fomin <maxim@maxim-fomin.ru> 2012-09-09 07:02:06 PDT ---
(In reply to comment #1)
> (In reply to comment #0)
> > void foo(int)
> > {
> > 
> > }
> > 
> > void main()
> > {
> >     foo(5);
> > }
> > 
> > Although anonymous function parameters may be used in function declarations, it seems that dmd doesn't check whether a function declaration is a definition too.
> 
> What's the problem here?
> 
> foo() not giving a name to its first argument means the programmer is stating
> foo() never uses its first argument, and the D language allows the programmer
> to enforce this desire.
> 
> This feature also allows to avoid "unused argument warnings" once/where such warning is available.

The problem is that such code is likely to be a bug (parameter name was forgotten) and compiler should report about this. BTW dmd doesn't produce any warning for unused variable.

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> BTW dmd doesn't produce any warning for unused variable.

And this will never change. ;)

On Sunday, 9 September 2012 at 19:59:02 UTC, Namespace wrote:
>> BTW dmd doesn't produce any warning for unused variable.
>
> And this will never change. ;)

Who knows, maybe eventually I'll be able to convince GDC maintainers to introduce this warning :-)

On Sunday, 9 September 2012 at 20:19:51 UTC, bearophile wrote:
> On Sunday, 9 September 2012 at 19:59:02 UTC, Namespace wrote:
>>> BTW dmd doesn't produce any warning for unused variable.
>>
>> And this will never change. ;)
>
> Who knows, maybe eventually I'll be able to convince GDC maintainers to introduce this warning :-)

But he said dmd. :P

http://d.puremagic.com/issues/show_bug.cgi?id=8634



--- Comment #3 from bearophile_hugs@eml.cc 2012-09-09 13:35:05 PDT ---
(In reply to comment #2)

> The problem is that such code is likely to be a bug (parameter name was forgotten) and compiler should report about this.

I care a lot about removing bug-prone situations from D language. And I think C# language acts as you ask. Generally C# designers are very careful in avoiding bug-prone features.

But in general it's not so common to forget to add a name for the argument. And even in the cases where I have forgotten to put the argument name, this is usually not a big problem, because the compiler doesn't find the name you are using inside the function, and gives you a nice compilation error at the first usage attempt, close enough to the function signature (unless your functions are really long).

In theory one bug-prone situation is when you use a name thinking it's the name of a local argument, while you have not given a name to the argument, and you have a name in an outer scope that is the same. So you are actually using the name of the outer scope. In practice my diary of bugs shows I have never hit this bug, also because it's generally a good practice to not define local names equal to outer names.

So unless you have evidence that this is a common enough bug (even few anecdotes are enough to keep this discussion open) I think this bug report should be closed.


> BTW dmd doesn't produce any warning for unused variable.

I know, but probably someday some D compiler will report them. It's an useful feature and it's not too much hard to implement. All the major C++ compilers have an option to report them.

But note here I was not referring to a generic "unused variable" warning, I was referring to more specifically to a "unused argument" warning. If you omit the argument name, the warning is silenced.

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Maxim Fomin <maxim@maxim-fomin.ru> changed:

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


--- Comment #4 from Maxim Fomin <maxim@maxim-fomin.ru> 2012-09-10 05:22:14 PDT ---
I have no desire for disputes about things which are not necessarily defective (as revealed here) and claimed by D people to be intentional part of the language.

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