Compile Time Tuple-ogy II

Implementing std::apply with compile-time tuple transformation

This Cracked C++ problem tests your command of compile-time metaprogramming: specifically, variadic templates, index sequences, and constexpr function composition. It sits at the intersection of template mechanics and functional programming patterns that high-performance C++ codebases rely on.

The core challenge is threading a callable through a tuple's heterogeneous elements at compile time, transforming each one and reassembling the results into a new tuple. Strong solutions leverage index-sequence unpacking and constexpr evaluation to ensure the entire operation compiles to efficient code with zero runtime overhead. You'll need to think carefully about template parameter deduction, pack expansion, and how to preserve type information across the transformation.

• Variadic template parameter packs and pack expansion
• std::index_sequence and integer sequence unpacking
• Constexpr functions and compile-time evaluation
• Template specialization and recursive instantiation