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

"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 =)

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

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

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

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

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