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C++20 Modules: Practical Insights, Status and TODOs

3 days ago
https://chuanqixu9.github.io/c++/2025/08/14/C++20-Modules.en.html
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  • #Compilation
  • #C++20
  • #Modules
  • C++20 Modules improve code modularity, encapsulation, compilation speed, and reduce library code size.
  • Compilation time savings with C++20 Modules range from 25% to 45%, with extreme cases showing up to 26x improvement.
  • C++20 Modules and Pre-Compiled Headers (PCH) are not equivalent; Modules have their own semantics and can produce object files.
  • Modules can reduce object file and library sizes but may not significantly affect final executable size.
  • Using C++20 Modules is feasible in Linux + Clang and Windows + MSVC environments, but adoption is slow due to refactoring costs and compiler issues.
  • Modules Wrapper allows projects to provide optional Modules without forcing downstream users to adopt them.
  • Key practices include choosing specific suffixes for wrapped libraries and using .cppm for importable module units.
  • Modules reduce compile time by avoiding repeated template instantiations and optimizing frontend processing.
  • Non-Cascading Changes in Clang help break dependency chain propagations, reducing unnecessary recompilations.
  • Issues like ODR violations and forward declaration problems need careful handling during module migration.
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