• AntonSotov (21/21) Jul 30 2016 import std.stdio;
• Seb (11/32) Jul 30 2016 just have a look with pragma(msg, T) what the compiler is
• AntonSotov (3/3) Jul 30 2016 2 Seb
• Andrew Godfrey (9/12) Jul 31 2016 An example of Seb's warning:

AntonSotov <nepuvive rainmail.biz> writes:

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?

Seb <seb wilzba.ch> writes:

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.

AntonSotov <nepuvive rainmail.biz> writes:

2 Seb

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

Andrew Godfrey <X y.com> writes:

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))