import std.stdio;

void myFunc(T)(in T val) {
    static if(is(T == string)) {
        writeln("string: ", val);
    }
    static if(is(T : long)) {
        writeln("long: ", val);
    }
    static if                         // WHAT HERE ?
        writeln("null");
    }
}

int main(string[] args)
{
    myFunc("abc");
    myFunc(123);
    myFunc(null);
    return 0;
}
//--------------------------------------------------
How to transfer <null> as parameter type?

On Sunday, 31 July 2016 at 05:22:40 UTC, AntonSotov wrote:
> import std.stdio;
>
> void myFunc(T)(in T val) {
>     static if(is(T == string)) {
>         writeln("string: ", val);
>     }
>     static if(is(T : long)) {
>         writeln("long: ", val);
>     }
>     static if                         // WHAT HERE ?
>         writeln("null");
>     }
> }
>
> int main(string[] args)
> {
>     myFunc("abc");
>     myFunc(123);
>     myFunc(null);
>     return 0;
> }
> //--------------------------------------------------
> How to transfer <null> as parameter type?

just have a look with pragma(msg, T) what the compiler is inferring ;-)
-> typeof(null) seems to be a Voldemord type that can't be expressed directly, hence you can do:

    static if(is(T : typeof(null))) {
        writeln("null");
    }

... but does this really help you? A string can be null too, so whatever you do you most likely should check that with `val is null` too.

2 Seb

Thank you!
is (T: typeof (null)) - very comfortable

On Sunday, 31 July 2016 at 05:41:55 UTC, AntonSotov wrote:
> 2 Seb
>
> Thank you!
> is (T: typeof (null)) - very comfortable

An example of Seb's warning:
What happens if you have:
string s = null;
MyFunc(s);

I'm guessing it doesn't do what you want. But it isn't clear what you want - null is a value, not a type. It's just as if you were saying:
is (T: typeof (-3))