What is SFINAE and how does it work?

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**SFINAE** — Substitution Failure Is Not An Error. When template argument deduction fails, the overload is silently removed. ```cpp // Enable if T has a size() method template auto print_size(const T& t) -> decltype(t.size()) { return t.size(); } // Falls back to this if SFINAE fails void print_size(...) { std::cout << "no size()"; } ``` **Modern alternative — std::enable_if:** ```cpp template std::enable_if_t, T> double_value(T x) { return x * 2; } ``` **Even better — C++20 concepts:** ```cpp template concept HasSize = requires(T t) { t.size(); }; void print(HasSize auto const& c) { std::cout << c.size(); } ``` **Use concepts over SFINAE for clarity.

C++: What is SFINAE and how does it work?