Enough TMP to write a Variant
summary
Claims a working std::variant reimplementation in C++20 that fits less than 500 lines and can be taught in an hour, with real support for multiple-dispatch, constexpr, noexcept and return-type deduction. Implementation uses a tagged union, std::construct_at/std::destroy_at, index_sequence math, unrolled get-by-index and a macro-generated jump-table switcher to avoid indirect calls. Error reporting uses a common-type-with-error-tag trick so SFINAE/Concept checks give compact messages. The result compiles and runs and the visit machinery produces optimized direct jumps rather than function-pointer indirection.
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chapters (11)
- 0:00Introduction
- 7:13Template metaprogramming basics
- 11:28Utility library for TMP
- 21:05Custom Union type
- 25:59Compile-time switch
- 31:15Variant data structure
- 36:14Return types and errors
- 41:12Finalizing visit
- 44:04Integrating components
- 46:10Summary
- 46:36Q&A
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