Why do some T.init evaluate to true while others to false?

[ArturG via Digitalmars-d-learn]

On Friday, 27 May 2016 at 18:03:23 UTC, Steven Schveighoffer 
wrote:

> I didn't change the default. The default is to pick the first 
> member and use that as the init value. I may not have even 
> considered what foo.init might be when I was creating my enum.
>
> -Steve

by default i ment this

enum foo
{
     bar
}
foo f;
if(f) "dosnt print".writeln;

but i understand what you mean which adds a problem to my 
checkThen template, as the return type of the template depends on 
the return type of the callable which right now returns the init 
value of the callable return type if the type you pass into the 
template evaluates to false.

an example:

class Foo { int x; }
Foo foo(){ return null; }

foo.checkThen!( f => f.x = 5; ).writeln; // writes f.x.init 
because i kinda need a common return type if foo wouldnt return 
null