Question

There is a well-known fact that C++ templates are turing-complete, CSS is turing-complete (!) and that the C# overload resolution is NP-hard (even without generics).

But is C# 4.0 (with co/contravariance, generics etc) compile-time turing complete?

Answer 1

Unlike templates in C++, generics in C# (and other .net lang) are a runtime generated feature. The compiler does do some checking as to verify the types use but, actual substitution happens at runtime. Same goes for Co and contravariance if I’m not mistaken as well as even the preprocessor directives. Lots of CLR magic.

(At the implementation level, the primary difference is that C#
generic type substitutions are performed at runtime and generic type
information is thereby preserved for instantiated objects)

See MSDN

http://msdn.microsoft.com/en-us/library/c6cyy67b(v=vs.110).aspx

Update:
The CLR does preform type checking via information stored in the metadata associated with the compiled assemblies(Vis-à-vis Jit Compliation), It does this as one of its many services,(ShuggyCoUk answer on this question explains it in detail) (others include memory management and exception handling). So with that I would infer that the compiler has a understanding of state as progression and state as in machine internal state (TC,in part, mean being able to review data (symbols) with so reference to previous data(symbols) , conditionally and evaluate) (I hesitated to state the exact def of TC as I, myself am not sure I have it fully grasped, so feel free to fill in the blanks and correct me when applicable ) So with that I would say with a bit of trepidation, yes, yes it can be.