is() and const

[Andrea Fontana]

Run this code:

class PP {}

void what(T)(T val)
{
        static if (is(T == int)) writeln ("T == int");
        static if (is(T == const(int))) writeln ("T == const(int)");
        static if (is(T : int)) writeln ("T : int");
        static if (is(T == PP)) writeln ("T == PP");
        static if (is(T == const(PP))) writeln ("T == const(PP)");
        static if (is(T : PP)) writeln ("T : PP");
}

void main(string[] args)
{

        const int aa = 10;
        int ab;
        
        const PP ba = new PP;
        PP bb = new PP;
        
        writeln("- Testing const(int)");
        what(aa);
        writeln();
        
        writeln("- Testing int");
        what(ab);
        writeln();
        
        writeln("- Testing const(PP)");
        what(ba);
        writeln();
        
        writeln("- Testing PP");
        what(bb);
        writeln();
        
        return;
}

It says:

- Testing const(int)
T == const(int)
T : int

- Testing int
T == int
T : int

- Testing const(PP)
T == const(PP)

- Testing PP
T == PP
T : PP


So:
const(int) : int  <-- true
const(PP) : PP  <-- false

Is this behaviour correct?

And how can I check if T is of a certain class ignoring consts (and
avoiding double checks)?