Is there a simple way to check if value is null for every case?

[rikki cattermole]

On 27/08/2018 4:37 AM, SG wrote:
> Hi again,
> 
> The code below works for some cases but not for the Nullable!Type.
> 
> A way to fix it should be check the type and use ".isNull" for 
> Nullabe!Type. But is there a simple way to test if value is null for 
> every case?
> 
> 
> import std.stdio, std.typecons, std.variant, std.conv;
> 
> bool foo(T)(T t){
>      return (t is null);
> }
> 
> class S{
>      Nullable!int i;
> }
> 
> void main(){
>      string x = "a";
>      writeln(x is null," - " ,x.foo);
> 
>      string y = null;
>      writeln(y is null," - ", y.foo);
> 
>      auto z = null;
>      writeln(z is null," - ", z.foo);
> 
> 
>      S s = new S();
>      writeln(s.i.isNull); // Ok
> 
>      //writeln(s.i is null); // Error
>      //s.i.foo(2); // Error
> }

UFCS function called isNull.

e.g.

import std.traits : isPointer;
bool isNull(T)(T value) if (is(T == class) || isPointer!T) {
	return value is null;
}