Disappointing inflexibility of argument passing in D

[Carl Sturtivant]

D has opAssign, making defining implicit conversions from any 
type to a new type possible on assignment, so where is the 
analogue (say opPass) for passing an argument to a function?

void f( Data d, Data2 d2) { ..... }

void main() {
        //conversions from string part of the definitions of Data, 
Data2
     f( "hello", "bonjour"); //no way to do this --- disappointing
}

See
http://forum.dlang.org/thread/agstjpezerwlgdhphclk@forum.dlang.org