• Sean Eskapp (12/12) Aug 06 2011 If I have something like
• Philippe Sigaud (9/21) Aug 07 2011 Yeah, function templates have a way to automatically determine their
• Ali =?iso-8859-1?q?=C7ehreli?= (22/40) Aug 07 2011 It has been the same in C++. The reason is that the syntax above would

Sean Eskapp <eatingstaples gmail.com> writes:

If I have something like

    struct S(T)
    {
        T data;
    }


I can't make a struct literal with

    int mystuff;
    someFunc(S(mystuff));

I have to use

    int mystuff;
    someFunc(S!(int)(mystuff));

Why is this?

Philippe Sigaud <philippe.sigaud gmail.com> writes:

On Sat, Aug 6, 2011 at 22:19, Sean Eskapp <eatingstaples gmail.com> wrote:
 If I have something like

 =C2=A0 =C2=A0struct S(T)
 =C2=A0 =C2=A0{
 =C2=A0 =C2=A0 =C2=A0 =C2=A0T data;
 =C2=A0 =C2=A0}

   I can't make a struct literal with

 =C2=A0 =C2=A0int mystuff;
 =C2=A0 =C2=A0someFunc(S(mystuff));

 I have to use

 =C2=A0 =C2=A0int mystuff;
 =C2=A0 =C2=A0someFunc(S!(int)(mystuff));

 Why is this?

Yeah, function templates have a way to automatically determine their
template parameters (IFTI : Implicit Function Template
Instantiation?), but that doesn't work with struct and class
constructors. Too bad.

You can use a factory function to do just that, it's a one-liner:

auto s(T)(T t) { return S!(T)(t); }

and then:

someFunc(s(mystuff));

Ali =?iso-8859-1?q?=C7ehreli?= <acehreli yahoo.com> writes:

On Sat, 06 Aug 2011 20:19:06 +0000, Sean Eskapp wrote:

 If I have something like
 
     struct S(T)
     {
         T data;
     }
 
 
 I can't make a struct literal with
 
     int mystuff;
     someFunc(S(mystuff));

It has been the same in C++. The reason is that the syntax above would 
conflict with and is reserved for a templated constructor.

 I have to use
 
     int mystuff;
     someFunc(S!(int)(mystuff));
 
 Why is this?

To allow flexibility by not tieing the struct's template parameters to 
its constructor's template parameters. Deduction actually works for the 
constructor:

struct S(T)
{
    T data;

    this(U)(U)
    {}
}

void someFunc(T)(T)
{}

void main()
{
    double d;
    someFunc(S!int(d));
}

The constructor's template parameter is being deduced as 'double' on the 
last line.

Ali