UDAs - Restrict to User Defined Types?

[Jonathan M Davis]

On Friday, November 09, 2012 01:53:40 Nick Sabalausky wrote:
> Looking at one set of interfaces in isolation, sure the chances might
> be low. (Just like the chances of name collisions when hygeine is
> lacking, and yet we thankfully have a real module system, instead of C's
> clumsy "Well, it should usually work ok!" garbage.) But it's a terrible
> precedent. Scale things up, use ducks as common practice, and all of a
> sudden you're right back into the same old land of "no-hygeine". Bad,
> sloppy, lazy precedent. AND the presumed benefit of the duckness is
> minimal at best. Just not a good design, it makes all the wrong
> tradeoffs.

As long as your template constraints requires more than a couple of functions 
and actually tests much of anything about what those functions return or what 
arguments can be passed to them, I find it very unlikely that anything will 
accidentally pass them. Too many coincidences would be required to end up with 
a set of functions that matched when they weren't supposed to . It's only 
likely to be problem if you're checking only one or two functions and don't 
check much beyond their existence. It just doesn't take very many checks 
before it's highly unlikely for anyone to have created a type with functions 
with the same names and whose signatures are close enough to pass a template 
constraint when they're not supposed to.

- Jonathan M Davis