Pure, Nothrow in Generic Programming

[dsimcha]

One issue that should ideally be resolved before D2 is finalized that I meant
to bring up here a long time ago is how to handle pure and nothrow in generic
functions.  For example:

T max(T)(T lhs, T rhs) {
    return (lhs > rhs) ? lhs : rhs;
}

Obviously, if T is an int, max can be pure nothrow.  However, if T is some
user defined type, then who knows?  I've run into a few cases where I'm
writing a pure function that needs to call something simple like
std.algorithm.max() on an int or a float and invariably I end up just
rewriting a max function for my specific type and marking it as pure nothrow.
 This is obviously a suboptimial solution.

Since the source needs to be available anyhow for templates to be usable, my
proposal would be for pure/nothrow functions to be able to call templated
functions that are not marked as pure/nothrow as long as they would compile if
marked pure/nothrow.  Also, I think that we need to establish a strong
convention, for objects, that opCmp, opEquals and a few other "standard"
functions should always be const pure nothrow, and that it is acceptable for
any library code (mixins, etc.) to assume this.