Create custom data types

[via Digitalmars-d-learn]

Another possible way is to check the bounds at compile time. The 
different operators need to be overloaded for that. For example, 
if you have to types Int!(0, 100) and Int!(20, 30), the result 
type of an addition needs to be Int!(20, 130).

Then, there can be an overloaded opCast() to bool for use with 
if():

Int!(20, 130) i;
if(auto j = i.checkBounds(20, 32)) {
     static assert(is(typeof(j) == Int!(20, 32)));
}