GoKawiilC++26 proposal adds native pre/post contract syntax to functions
A technical walkthrough demonstrates how C++26 introduces built-in 'contracts' syntax, letting developers express function preconditions directly in a function's signature using pre(...), rather than relying on assert() calls buried inside the implementation. The example shows a get_value function checking that an index is within a vector's bounds, with the condition visible in both declaration and definition.
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Moving such checks into the language itself could make API requirements visible to anyone reading a header file, rather than hidden inside implementation code, which may reduce misuse of library functions. Because contract checking can be toggled via compiler options rather than macros like NDEBUG, this suggests more consistent and standardized enforcement of correctness checks across codebases than today's assert-based approach allows.
- C++26 introduces pre(...) syntax to attach preconditions directly to function signatures
- Contracts can appear in both declarations and definitions, unlike assert-based checks confined to .cpp files
- The feature builds on prior Standard Library hardening work discussed in an earlier related article
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Published there as: “C++26 Contracts: Introduction to Preconditions and Postconditions”
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