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digitalmars.D.bugs - [Issue 5804] New: map! needs to fail on void functions + I'd like a mapCall function

reply d-bugmail puremagic.com writes:
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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Mar 31 2011
next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=5804


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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Apr 01 2011
prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=5804


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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Apr 24 2011
prev sibling next sibling parent d-bugmail puremagic.com writes:
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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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prev sibling next sibling parent d-bugmail puremagic.com writes:
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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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Apr 24 2011
prev sibling parent d-bugmail puremagic.com writes:
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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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