template type check syntax

[gzp]

Which is the preferred form ? Shall I place the static assert into the 
in part or into the body directly ?

Is there any difference ? Is there a way to toggle if the in part is 
executed/compiled or not ?  - Like in eifel it can be turned on and off 
by a compiler flag.

template check1(T) {
        enum check1 = ...;
}

bool check2(T t) {
        return ...;
}


void foo(T)(ref T t)
in {
        static assert( check1!(T) );
        assert(check2(t);
}
body {
        static assert( check1!(T) );
...
}


Or is there a form like (As i've seen mentioned with future coming opBinary)
void foo(T)(ref T t) if check1!(T)
{
        in {
                assert(check2(t);
        }
        body {
                ...
        }
}


Thanks,
Gzp