Template Constraints

[Jonathan via Digitalmars-d-learn]

I am having trouble finding many useful explanations of using 
template constraints beyond basic usage.

I would like to have a template constrant to enforce that a type 
can be explicitly cast to another type:

    void (T)(T t)
            if (cast(int) T)//force `cast(int) T` to be possible
        {
            // Yay I know `t` can be cast to an `int`!
    }

Is this possible?