This is a small C++ program that compiles:

template<typename T> struct Foo {
    Foo(T x) {}
    template<typename U> void operator()(U y) {}
};
int main() {
    Foo<int> foo(1);
    foo(1.5);
}


I think this is an equivalent D2 program:

struct Foo(T) {
    this(T x) {}
    void opCall(U)(U y) {}
}
void main() {
    auto foo = Foo!int(1);
    foo(1.5);
}


But dmd 2.046 prints:
temp.d(7): Error: constructor temp.Foo!(int).Foo.this (int x) is not callable using argument types (double)
temp.d(7): Error: cannot implicitly convert expression (1.5) of type double to int

Is this a bug in my D code? If it's a bug in my D code, do you know how to translate that C++ code in D2?

Bye and thank you,
bearophile

On Sun, May 30, 2010 at 17:04, bearophile <bearophileHUGS@lycos.com> wrote:

> struct Foo(T) {
>    this(T x) {}
>    void opCall(U)(U y) {}
> }
> void main() {
>    auto foo = Foo!int(1);
>    foo(1.5);
> }
>

I've had this one too. I think it's a bug, because foo is already
constructed when foo(1.5) is used. So the compiler should know it's an
opCall and not a constructor call.
The only solution I found was a kludge:


struct Foo(T)
{
   void initialize(T)(T x) {} // in my case, their was some data
initialization there.
   void opCall(U)(U y) {}
}

Foo!T foo(T)() { Foo!T f; f.initialize(); return f;}

void main() {
    auto f = foo(1);
   f(1.5);
}


Philippe

Hello bearophile,

> struct Foo(T) {
> this(T x) {}
> void opCall(U)(U y) {}
> }
> void main() {
> auto foo = Foo!int(1);
> foo(1.5);
> }

FWIW, The struct being a template is extraneous.

> temp.d(7): Error: constructor temp.Foo!(int).Foo.this (int x) is not callable 
using argument types (double)

The lookup seems to think you are calling the constructor. Should make it easy to find the bug. (And yes, I think this is a bug)

-- 
... <IXOYE><

BCS:
> FWIW, The struct being a template is extraneous.

You are right, thank you. I have added the simplified example: http://d.puremagic.com/issues/show_bug.cgi?id=4253

Bye,
bearophile

On Sun, May 30, 2010 at 18:31, bearophile <bearophileHUGS@lycos.com> wrote:

> BCS:
> > FWIW, The struct being a template is extraneous.
>
> You are right, thank you. I have added the simplified example: http://d.puremagic.com/issues/show_bug.cgi?id=4253
>
>
This one had me gnashing my teeth. I voted it up.


Philippe