templateswitching

Template switching is a technique in template metaprogramming that selects among multiple template implementations or behaviors at compile time based on properties of type parameters or non-type template parameters. It enables different code paths to be chosen automatically for different types without runtime overhead.

Common mechanisms include template specialization and overloading, the use of SFINAE (substitution failure is not an error) with type traits such as is_integral or is_floating_point, tag dispatch, and, in modern compilers, if constexpr–based branching. The goal is to provide a single interface that adapts its behavior to the concrete types it is instantiated with, without incurring runtime overhead.

Examples can be implemented in several ways. In C++11/14, one approach uses overloading and enable_if to create separate implementations for integral and floating-point types. For instance, a function template can be provided in two versions, each enabled only for the corresponding type category. In C++17 and later, if constexpr allows emptying the branching into a single template while selecting paths at compile time based on type traits.

Applications of template switching include generic libraries, numeric algorithms, and policy-based designs where behavior depends on type traits. It supports efficient, type-safe customization without sacrificing performance, but can increase compilation time and code size, and may reduce readability if overused. See also template metaprogramming, SFINAE, tag dispatch, and constexpr if.