Modern Template Techniques (C++17)

Volume 1 covered the "mechanism" of templates: the compilation model, specialization, CRTP. This part covers the modern tools C++17 brought to template engineering. if constexpr lets a template dispatch by type without a pile of overloads, variadic templates handle any number of arguments, perfect forwarding lets a generic factory pass arguments through untouched, and CTAD saves you from writing out every angle bracket. A type-safe any at the end welds these together.

One thing to flag up front: the old TMP toolkit (type traits, SFINAE, void_t, fold expressions) lives in the metaprogramming sub-volume, in the "TMP Core Techniques" piece (it's the prelude to concepts). This part doesn't repeat it.

Runnable examples live in code/examples/vol4/vol2-modern-cpp17/. Each file compiles with g++ -std=c++17 xxx.cpp.

if constexpr: Compile-Time Branching→Variadic Templates: Expanding Parameter Packs→Perfect Forwarding: Forwarding References and Reference Collapsing→CTAD: Class Template Argument Deduction→Capstone Project: A Type-Safe any→Designated Initializers→C++20 Ranges Library Basics and Views→Pipeline Operations and Ranges in Practice→

Pieces 01 through 05 are the spine of the C++17 template line. if constexpr opens, on why compile-time branching replaces a stack of overloads; 02 takes apart the expansion of parameter packs (recursion, if constexpr termination, and fold, compared side by side); 03 covers perfect forwarding and reference collapsing, machinery no generic factory can avoid; 04 is CTAD, how the compiler back-infers template arguments from constructor arguments; 05 closes with a hand-written type-safe any that ties the previous four together. Pieces 06 through 08 are a few other modern features in this volume (designated initializers and Ranges); they're earlier in style and don't quite match 01 through 05, left for a later cleanup pass.