Conversion between composite types

gistfile1.d

/**
Object-to-object conversion converts each field in turn. Possible conversions are
between tuples, structs and classes. Target class must have a default constructor.
*/
T toImpl(T, S)(S src)
    if (!isImplicitlyConvertible!(S, T) &&
        !is(typeof(T(src))) && !is(typeof(new T(src))) && // don't conflict with converting construction
        !isAssociativeArray!T && !isAssociativeArray!S && // don't conflict with AA conversion
        !is(typeof(S.init.opCast!T()) : T) &&             // don't conflict with opCast conversion
        !is(T == union) && !is(S == union) &&             // unions not supported
        is(typeof(T.tupleof)) && is(typeof(S.tupleof)))
{
    static if (is(T == class))
        T result = new T();
    else
        T result;
    foreach (i, v; src.tupleof)
        result.tupleof[i] = to!(typeof(result.tupleof[i]))(v);
    return result;
}