Mixin Macros Pattern

From David Simcha's D-Specific Design Patterns talk at DConf 2013.

Problem: Repetitive code with slight variations

Example: Arithmetic operator overloading

Want:

• Minimal code duplication
• Ability to use templates/CTFE
• (Avoid (Lispy (syntax)))

Solution: Mixins + Compile-Time Magic

// D's operator overloading was designed around mixins
struct Int 
{
    Int opBinary(string op)(Int rhs)
    {
       int value = mixin("value_ " ~ op ~ " rhs.value_");
       return Int(value);
    }

    int value() @property 
    { 
        return value_; 
    }

    private int value_;
}

void main()
{
    assert((Int(2) - Int(5)).value == -3);
    assert((Int(2) + Int(4)).value == 7);
}