Why I want Concepts, sooner rather than later
I was involved in putting concepts into the g++ standard library, for the aborted C++0x concept design.<p>My feeling is this is a classic example of an area where the perfect is the enemy of the good.<p>At one extreme we have C++&#x27;s current design -- try substituting the types into the template and see what explodes. At the other extreme (which is what C++0x templates did) is that if a template passes &#x27;concept check&#x27;, we know, 100%(ish), that the resulting code is going to compile.<p>The problem is, that this means when you write the concepts for a function, you have to have concepts for every corner of the C++ language you could make use of. This means for many functions the concept list ended up being longer than the function! Further, it is easy to miss optimisations (such as rvalue references), because you didn&#x27;t &#x27;concept&#x27; for them.<p>The latest aim is (to me) a good middle-ground. It checks (for example) that something is &quot;numberish&quot;, or &quot;iteratorish&quot;. You can easily create freakish types which will pass concept check, and then not compile, leading to the kind of error messages users currently get. But the common cases, of people passing sensible, but wrong, things into methods, will get much nicer errors.