template constraint diagnostics

[Vlad Levenfeld via Digitalmars-d]

I have something like this for mixin interfaces that require that 
the host struct support certain semantics. There's a Traits 
struct (concept-ish) that takes a set of strings for trait 
identifiers and their definitions (which is some code that 
compiles if and only if the trait is satisfied).

The Traits struct has a member mixin template, "require", which 
can be used by the interface that instantiated the Traits. When 
one of the mixed-in requirements is failed, the compiler 
generates an error message like this:

source/evx/meta/traits/generator.d-mixin-49(50): Error: static 
assert  "MyStruct must support {size_t x = buffer.length;} to 
enable TransferOps."

Not as nice as a compiler-aided concept solution but I have been 
pretty happy with it so far. It doesn't take me long to forget 
what some interface requirements are, and this way the compiler 
can explicitly guide me.