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digitalmars.D.bugs - [Issue 8402] New: Lambda argument's default value is not taken into account

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8402

           Summary: Lambda argument's default value is not taken into
                    account
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: kolos80 bk.ru



---
The following code does not compile (x.d):

void main()
{
    auto fn = (int x = 0) => x + 1;
    fn();
}

with message: "x.d(4): Error: expected 1 function arguments, not 0"
However, calling fn() with an explicit argument works fine as usual.

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Jul 20 2012
next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8402


Jonathan M Davis <jmdavisProg gmx.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jmdavisProg gmx.com



PDT ---
Default arguments with lambda functions don't really make sense given that
they're generally only used in one place, that default arguments are _not_ part
of the type (they're just inserted at the call site), and that there's no way
for lambdas or function pointers to carry default arguments with them. So, the
fact that it doesn't compile is a _good_ thing, though it really should give an
error for giving a default argument and not just an error at the call site.


duplicate or not.

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Jul 20 2012
prev sibling next sibling parent d-bugmail puremagic.com writes:
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Erik Johansson Andersson <exetoc gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |exetoc gmail.com



14:27:43 PDT ---
This seems to be relevant:

void function(int i = 0) f = (int i){};
void delegate(int i = 0) g = (int i){};

void main()
{   
    f();
    g();
}

The error message is: "Error expected 1 function arguments, not 0", for both f
and g.



 Default arguments with lambda functions don't really make sense given that
 they're generally only used in one place, that default arguments are _not_ part
 of the type (they're just inserted at the call site), and that there's no way
 for lambdas or function pointers to carry default arguments with them. So, the
 fact that it doesn't compile is a _good_ thing, though it really should give an
 error for giving a default argument and not just an error at the call site.
 

 duplicate or not.


It did work in 2.059, which was nice, because it allowed libraries like
Derelict to provide bindings for C++ libraries like FreeImage, without having
to modify the interface in order to take into account potential default
arguments which, as of 2.060, isn't the case anymore. Did this old behaviour
have any negative effects at all?

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Aug 02 2012
prev sibling next sibling parent d-bugmail puremagic.com writes:
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timon.gehr gmx.ch changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |timon.gehr gmx.ch





 Did this old behaviour have any negative effects at all?


Probably the feature was there by mistake. It was implemented incorrectly. I 
think just associating the default arguments with the variable declaration
might 
work if something like it should be supported.

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Aug 02 2012
prev sibling next sibling parent d-bugmail puremagic.com writes:
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20:04:56 PDT ---
I was referring to variables (and not literals) in the latter part of my
comment, whereas you probably didn't. If that is indeed the case, then
disregard what I said.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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 The following code does not compile (x.d):
 
 void main()
 {
     auto fn = (int x = 0) => x + 1;
     fn();
 }
 
 with message: "x.d(4): Error: expected 1 function arguments, not 0"
 However, calling fn() with an explicit argument works fine as usual.


The function pointer `fn` is not a lambda itself, so cannot have default
argument.
If it is allowed:

    auto fn = (int x = 0) => x + 1;
    fn();   // returns 1

    fn = (int x = 1) => x + 1;
    fn();   // returns 1 or 2?

What is returned by the 2nd call of fn? I cannot imagine it.

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Aug 04 2012
prev sibling parent d-bugmail puremagic.com writes:
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Kenji Hara <k.hara.pg gmail.com> changed:

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



This issue is a part of bug 3866.

*** This issue has been marked as a duplicate of issue 3866 ***

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