TLDR
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Walks through applying Alexis King’s parse-don’t-validate paradigm to a date parser across C++98, C++11, C++17, and C++23.
Key Takeaways
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The core idea: use the type system so a successfully constructed type is already valid, eliminating downstream validation branches.
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C++98 version uses a private constructor, enum-based
ParseStatus, no heap allocation, and no exceptions, suitable for embedded targets.
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C++11 version delegates parsing to
std::get_time and uses exceptions for failure; C++17 swaps exceptions for std::optional return values.
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C++23 introduces
std::expected for rich error information without exceptions, the clearest expression of the pattern in the series.
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A private constructor is the enforcement mechanism across all versions: invalid
Birthdate instances simply cannot be constructed.
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