template and constraints

[bioinfornatics]

I got a little problem with these code:

____________________
double div(T a, U b)() if( a > 0 && b > 0 ){ // not works T and U unknwn
identifier
    return a / b;
}
double div(T,U)(T a, U b) if( a > 0 && b > 0 ){ // not works, a  and b
not known at compile time
    return a / b;
}

double div(double a, double b)() if( a > 0 && b > 0 ){ // works but not
generic
    return a / b;
}
_____________________


The only one who works is a not generic! they are a way? or i need to
write for each parameter type?