This seems vaugely similar to C# Code Contracts. The difference there is that it was embedded as an assertion into the method: Contract.Requires(start > 0)

This seems vaugely similar to C# Code Contracts. The difference there is that it was embedded as an assertion into the method: Contract.Requires(start > 0); Contract.Ensures(someReturn != null); I loved it. It gave you much (not all) of that "if it compiles it works" good vibes that Rust has. Though, oh boy, were you in for a surprise if you think that Rust compiles slowly. You could probably do something similar with C: CONTRACT_REQUIRE(x == 0 || x == -1); if(x) { void* result = malloc(1); CONTRACT_ENSURE(result != null); CONTRACT_CALLER(free(result)); return result; } else { CONTRACT_ENSURE(result == 0); return 0; } The nice thing about that is you could have a compatibility .h that asserts/nops the macros, making the code compile in ignorant compilers.