Specialization: Full, Partial, and Variable Templates
Give specific types exactly the implementation they deserve — the mechanism under std::hash, std::less, and every optimized fast path.
A primary template states the general algorithm; a specialization replaces it for specific arguments. The library uses this everywhere: std::hash<std::string> is a specialization of std::hash<T>.
Full specialization
One concrete argument list, template <>:
template <class T> struct Serializer {
static std::string dump(const T&) { return "generic"; }
};
template <> struct Serializer<bool> {
static std::string dump(const bool& b) { return b ? "true" : "false"; }
};
Partial specialization
Still templated, but constrained — a pattern, not a point:
template <class T> struct Serializer<std::vector<T>> {
static std::string dump(const std::vector<T>& v);
};
The compiler picks the most specialized match. This is how Capacity<std::array<T, N>> can read N out of the type.
Variable templates
A compile-time value parameterized by type:
template <class T> inline constexpr bool is_small_v = sizeof(T) <= 8;
Pairs naturally with specialization: give Rank<T> per-type values, expose rank_v<T>.
Design rule: specialize for behavior the type cannot express with its own members (external traits). If the behavior belongs inside the type, write a member instead.