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digitalmars.D.learn - Problem with ReturnType

reply bearophile <bearophileHUGS lycos.com> writes:
After an 1+ hours long bug hunt, I have reduced my code to the following one.
ReturnType below is a reduced version of std.traits.ReturnType:

template ReturnType(T) {
    static if (is(T R == return))
        alias R ReturnType;
}

void bar(T)(T f) { return f(); }

void main() {
    alias ReturnType!( typeof( (int x){ return x; } ) ) TInt; //problem
    bar((int n=1) { return 2; });
}

The output:
test.d(6): Error: expected 1 arguments, not 0
test.d(10): template instance test.bar!(int delegate(int x)) error instantiating

Is this a bug of DMD/Phobos (I am using 1.028)?

Bye,
bearophile
Apr 02 2008
next sibling parent "Neil Vice" <sardonicpresence gmail.com> writes:
"bearophile" <bearophileHUGS lycos.com> wrote in message 
news:ft14od$22lv$1 digitalmars.com...

 After an 1+ hours long bug hunt, I have reduced my code to the following 
 one.
 ReturnType below is a reduced version of std.traits.ReturnType:

 template ReturnType(T) {
    static if (is(T R == return))
        alias R ReturnType;
 }

 void bar(T)(T f) { return f(); }

 void main() {
    alias ReturnType!( typeof( (int x){ return x; } ) ) TInt; //problem
    bar((int n=1) { return 2; });
 }

 The output:
 test.d(6): Error: expected 1 arguments, not 0
 test.d(10): template instance test.bar!(int delegate(int x)) error 
 instantiating

 Is this a bug of DMD/Phobos (I am using 1.028)?

 Bye,
 bearophile



How bizarre... I just tried your code and it would appear that somehow the 
presence of the alias/ReturnType call causes the default parameter value in 
the subsequent line to be seemingly ignored...

Passing a parameter to the call to f() in bar, eliminating the alias line 
and removing the parameter from the delegate passed to bar all eliminate the 
error.

I don't see how this could be anything other than a very unusual compiler 
bug. Happy bug reporting =)
Apr 02 2008
prev sibling next sibling parent reply janderson <askme me.com> writes:
bearophile wrote:

 After an 1+ hours long bug hunt, I have reduced my code to the following one.
 ReturnType below is a reduced version of std.traits.ReturnType:
 
 template ReturnType(T) {
     static if (is(T R == return))
         alias R ReturnType;
 }
 
 void bar(T)(T f) { return f(); }



There is no return type.  alias Return is returning an int.


 
 void main() {
     alias ReturnType!( typeof( (int x){ return x; } ) ) TInt; //problem
     bar((int n=1) { return 2; });
 }
 
 The output:
 test.d(6): Error: expected 1 arguments, not 0
 test.d(10): template instance test.bar!(int delegate(int x)) error
instantiating
 
 Is this a bug of DMD/Phobos (I am using 1.028)?
 
 Bye,
 bearophile
Apr 04 2008
parent reply bearophile <bearophileHUGS lycos.com> writes:
janderson:

 There is no return type.  alias Return is returning an int.



I know, that code isn't the minimal yet, but even if you replace bar with:

void bar(T)(T f) { f(); }

The situation doesn't change.

Bye,
bearophile
Apr 04 2008
parent janderson <askme me.com> writes:
bearophile wrote:

 janderson:

 There is no return type.  alias Return is returning an int.



 I know, that code isn't the minimal yet, but even if you replace bar with:
 
 void bar(T)(T f) { f(); }
 
 The situation doesn't change.
 
 Bye,
 bearophile



My bad.  It does look like a compiler deficiency.

-Joel
Apr 04 2008
prev sibling parent reply Kirk McDonald <kirklin.mcdonald gmail.com> writes:
bearophile wrote:

 After an 1+ hours long bug hunt, I have reduced my code to the following one.
 ReturnType below is a reduced version of std.traits.ReturnType:
 
 template ReturnType(T) {
     static if (is(T R == return))
         alias R ReturnType;
 }
 
 void bar(T)(T f) { return f(); }
 
 void main() {
     alias ReturnType!( typeof( (int x){ return x; } ) ) TInt; //problem
     bar((int n=1) { return 2; });
 }
 
 The output:
 test.d(6): Error: expected 1 arguments, not 0
 test.d(10): template instance test.bar!(int delegate(int x)) error
instantiating
 
 Is this a bug of DMD/Phobos (I am using 1.028)?
 
 Bye,
 bearophile



Delegates can't have default arguments.

-- 
Kirk McDonald
http://kirkmcdonald.blogspot.com
Pyd: Connecting D and Python
http://pyd.dsource.org
Apr 04 2008
parent bearophile <bearophileHUGS lycos.com> writes:
Kirk McDonald:

 Delegates can't have default arguments.



I don't understand much. I think what you say isn't enough to justify that
error, you may comment out some of those lines of code to see the results. But
maybe I just don't understand you.

Bye and sorry,
bearophile
Apr 04 2008