http://d.puremagic.com/issues/show_bug.cgi?id=5804

           Summary: map! needs to fail on void functions + I'd like a
                    mapCall function
           Product: D
           Version: unspecified
          Platform: Other
        OS/Version: Windows
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: Phobos
        AssignedTo: nobody@puremagic.com
        ReportedBy: andrej.mitrovich@gmail.com


--- Comment #0 from Andrej Mitrovic <andrej.mitrovich@gmail.com> 2011-03-31 18:57:51 PDT ---
import std.stdio;
import std.algorithm;

void mapCall(alias func, T)(T t)
{
    foreach (value; t)
    {
        func(value);
    }
}

void main()
{
    // nothing happens
    map!(writeln)([4, 5, 6]);

    // prints 4\n, 5\n, 6\n
    mapCall!(writeln)(4, 5, 6);
}

map doesn't work properly with void functions, it should at least check the return type of a function and fail to instantiate if the return type is void. Otherwise it seems like this is a no-op since nothing really happens.

The feature request is to either expand map! to work on void functions, or introduce a new function which allows us to call a single function in sequence with various arguments. The `mapCall` implementation here is just a demonstration, as is its name.

I think this type of function could be a useful to have, unless something like this already exists in Phobos (well, map was supposed to be it but it doesn't work for void functions..).

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Vladimir <thecybershadow@gmail.com> changed:

           What    |Removed                     |Added
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                 CC|                            |thecybershadow@gmail.com


--- Comment #1 from Vladimir <thecybershadow@gmail.com> 2011-04-01 01:23:15 PDT ---
Looks like a duplicate of issue 5753.

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Pedro Rodrigues <pdfrodrigues@gmail.com> changed:

           What    |Removed                     |Added
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                 CC|                            |pdfrodrigues@gmail.com


--- Comment #2 from Pedro Rodrigues <pdfrodrigues@gmail.com> 2011-04-24 06:02:19 PDT ---
Void functions imply side effects. According to the documentation map! does lazy evaluation. In my experience, mixing up lazy evaluation with side effects should be avoided at all costs. That's why I think that map! should be used with pure functions only and reject promptly void functions.

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bearophile_hugs@eml.cc changed:

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


--- Comment #3 from bearophile_hugs@eml.cc 2011-04-24 06:52:30 PDT ---
I suggest to merge this with bug 5753 , or the other way around.

Now pure functions are allowed to have a debug{} that contains impure code (for debug prints only, please), this decreases a little the need for impure functions.

In bug 5756 I have asked for eager amap()/afilter(), that's more fit for an
impure mapping function.

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--- Comment #4 from Pedro Rodrigues <pdfrodrigues@gmail.com> 2011-04-24 12:26:24 PDT ---
(In reply to comment #3)
> I suggest to merge this with bug 5753 , or the other way around.

I agree. I proposed a fix in issue 5753.

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Andrej Mitrovic <andrej.mitrovich@gmail.com> changed:

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


--- Comment #5 from Andrej Mitrovic <andrej.mitrovich@gmail.com> 2011-04-24 12:31:29 PDT ---
*** This issue has been marked as a duplicate of issue 5753 ***

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