"Contract support" is one of the things actively developed for C++.

Contracts, Preconditions & Invariants

By Andrzej Krzemienski

About the article

This blog post is an introductory material, demonstrating what a contract is, how preconditions and invariants can be derived from the contract, and how this process can help detect bugs. Two points stressed in this post are: (1) preconditions and invariants are not “contracts” and (2) only a subset of contract-related bugs can be detected through preconditions and invariants.