C++SFINAE与enable_if应用

CSFINAE与enable_if应用SFINAE替换失败不是错误是C模板元编程的核心技术允许在模板实例化失败时选择其他重载。enable_if根据条件启用或禁用模板。SFINAE原则模板替换失败不会导致编译错误。#include#include#includetemplatetypename std::enable_if::value, void::typeprocess(T value) {std::cout Integer: value * 2 \n;}templatetypename std::enable_if::value, void::typeprocess(T value) {std::cout Float: value * 1.5 \n;}templatetypename std::enable_if::value, void::typeprocess(T value) {std::cout Pointer: *value \n;}void sfinae_basic() {process(42);process(3.14);int x 100;process(x);}enable_if的返回类型位置。templateauto half(T value) - typename std::enable_if::value, T::type {return value / 2;}templateauto half(T value) - typename std::enable_if::value, T::type {return value / 2.0;}void enable_if_return() {std::cout Half int 10: half(10) \n;std::cout Half double 10: half(10.0) \n;}enable_if在模板参数中。template::value, int::type 0T add(T a, T b) {return a b;}void enable_if_param() {std::cout add(3, 4): add(3, 4) \n;std::cout add(2.5, 3.5): add(2.5, 3.5) \n;}检测类型是否有特定成员。templateclass has_size {templatestatic auto test(int) - decltype(std::declval().size(), std::true_type{});templatestatic std::false_type test(...);public:static constexpr bool value decltype(test(0))::value;};templateclass has_iterator {templatestatic auto test(int) - decltype(std::declval().begin(), std::true_type{});templatestatic std::false_type test(...);public:static constexpr bool value decltype(test(0))::value;};void member_detection() {std::cout vector has size: has_size::value \n;std::cout int has size: has_size::value \n;std::cout vector has iterator: has_iterator::value \n;std::cout int has iterator: has_iterator::value \n;}enable_if实现类型特征。templatestruct EnableIf {};templatestruct EnableIf {using type T;};templatestruct IsSame {static constexpr bool value false;};templatestruct IsSame {static constexpr bool value true;};void custom_traits() {static_assert(IsSame::value);static_assert(!IsSame::value);std::cout Custom traits work\n;}void conversion_type_traits() {std::cout is_void_v: std::is_void_v \n;std::cout is_array_v: std::is_array_v \n;std::cout is_enum_v: std::is_enum_v \n;std::cout is_class_v: std::is_class_v \n;}SFINAE can be used for tag dispatching.templatevoid advanced_process(T value, std::true_type) {std::cout Integer type: value * 2 \n;}templatevoid advanced_process(T value, std::false_type) {std::cout Non-integer type: value \n;}templatevoid advanced_process(T value) {advanced_process(value, std::is_integral{});}void tag_dispatch() {advanced_process(42);advanced_process(3.14);advanced_process(hello);}void sfinae_with_decltype() {auto lambda [](auto container) - decltype(container[0]) {return container[0];};std::vector vec {10, 20, 30};std::cout First element: lambda(vec) \n;}SFINAE是实现泛型类型检查和模板特化的重要技术广泛应用于标准库实现中。