Weird template instantiation speed?

[IchorDev]

While working on some new bindings, I've discovered that if 
`opAssign` in a struct template "`BindingTempl(T)`" has the 
return type "`BindingTempl!T` then it adds about 4 seconds to the 
compile time per instantiation of `BindingTempl`. The added 
compile time is much lower if a function other than `opAssign` 
returns `BindingTempl!T`. Is opAssign a particularly bad operator 
to overload in templates or something?