Function Templates

A function template is a recipe the compiler stamps out per type. You write the algorithm once; the compiler writes the type-specific versions.

template <typename T>
T max_of(const T& a, const T& b) {
    return a < b ? b : a;   // T must support operator< — that's the contract
}

int i = max_of(3, 7);          // T = int (deduced)
double d = max_of(2.5, 1.5);   // T = double
auto m = max_of(std::string{"a"}, std::string{"b"});

Key mechanics:

• Deduction happens from the arguments; explicit spelling max_of<double>(3, 7) forces it (and permits conversions).
• The contract is implicit: whatever operations the body uses become requirements on T. A type without operator< fails at instantiation — with a long error, but at compile time, never at runtime.
• Two-phase translation: the template itself is only syntax-checked; each instantiation is fully checked against the real T.
• Templates live in headers. The compiler needs the definition at the point of instantiation — a .cpp definition produces linker errors.