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#include <type_traits>
#include <iostream>
 
//
// My own addition to type traits
//
 
// Just a set of types
template <class... Args>
struct types {};
 
// true_type if T matches any types in Args, false_type otherwise.
template <class T, class... Args>
struct is_any;
 
template <class T, class Head, class... Tail>
struct is_any<T, Head, Tail...> : std::integral_constant<bool, is_any<T, Tail...>::value>
{};
 
template <class T, class... Tail>
struct is_any<T, T, Tail...> : std::true_type
{};
 
template <class T>
struct is_any<T> : std::false_type
{};
 
template <class T, class... Args1, class... Args2>
struct is_any<T, types<Args1...>, Args2...> : std::integral_constant<bool, is_any<T, Args1...>::value || is_any<T, Args2...>::value>
{};
 
// Here's a shortcut, because having this syntax in every function I write is painful.
template <class T, class... Args>
using enable_types = typename std::enable_if<is_any<T, Args...>::value>::type*;
 
//
// Testing
//
 
struct red {};
struct green {};
struct blue {};
struct cereal {};
struct icecream {};
struct pizza {};
struct tire {};
struct engine {};
struct transmission {};
 
using color_category = types<red, green, blue>;
using food_category = types<cereal, icecream, pizza>;
using part_category = types<tire, engine, transmission>;
 
template <typename T> 
void categorize(enable_types<T, color_category> = 0)
{
    std::cout << "T is a color" << std::endl;
}
 
template <typename T>
void categorize(enable_types<T, food_category, part_category> = 0)
{
    std::cout << "T is a food or a part" << std::endl;
}
 
template <typename T>
void categorize(enable_types<T, float, double, int> = 0)
{
    std::cout << "T is a float, double, or an int" << std::endl;
}
 
int main()
{
    categorize<int>();
    categorize<red>();
    categorize<icecream>();
    categorize<tire>();
    return 0;
}
 

prog.cpp:34:1: error: expected unqualified-id before 'using'
prog.cpp:50:7: error: expected nested-name-specifier before 'color_category'
prog.cpp:50:7: error: 'color_category' has not been declared
prog.cpp:50:22: error: expected ';' before '=' token
prog.cpp:50:22: error: expected unqualified-id before '=' token
prog.cpp:51:7: error: expected nested-name-specifier before 'food_category'
prog.cpp:51:7: error: 'food_category' has not been declared
prog.cpp:51:21: error: expected ';' before '=' token
prog.cpp:51:21: error: expected unqualified-id before '=' token
prog.cpp:52:7: error: expected nested-name-specifier before 'part_category'
prog.cpp:52:7: error: 'part_category' has not been declared
prog.cpp:52:21: error: expected ';' before '=' token
prog.cpp:52:21: error: expected unqualified-id before '=' token
prog.cpp:55:17: error: variable or field 'categorize' declared void
prog.cpp:55:17: error: 'enable_types' was not declared in this scope
prog.cpp:55:31: error: expected primary-expression before ',' token
prog.cpp:55:33: error: 'color_category' was not declared in this scope
prog.cpp:55:49: error: expected primary-expression before '=' token
prog.cpp:61:17: error: variable or field 'categorize' declared void
prog.cpp:61:17: error: 'enable_types' was not declared in this scope
prog.cpp:61:31: error: expected primary-expression before ',' token
prog.cpp:61:33: error: 'food_category' was not declared in this scope
prog.cpp:61:48: error: 'part_category' was not declared in this scope
prog.cpp:61:63: error: expected primary-expression before '=' token
prog.cpp:67:17: error: variable or field 'categorize' declared void
prog.cpp:67:17: error: 'enable_types' was not declared in this scope
prog.cpp:67:31: error: expected primary-expression before ',' token
prog.cpp:67:33: error: expected primary-expression before 'float'
prog.cpp:67:40: error: expected primary-expression before 'double'
prog.cpp:67:48: error: expected primary-expression before 'int'
prog.cpp: In function 'int main()':
prog.cpp:74:5: error: 'categorize' was not declared in this scope
prog.cpp:74:16: error: expected primary-expression before 'int'
prog.cpp:74:16: error: expected ';' before 'int'
prog.cpp:75:19: error: expected primary-expression before '>' token
prog.cpp:75:21: error: expected primary-expression before ')' token
prog.cpp:76:24: error: expected primary-expression before '>' token
prog.cpp:76:26: error: expected primary-expression before ')' token
prog.cpp:77:20: error: expected primary-expression before '>' token
prog.cpp:77:22: error: expected primary-expression before ')' token

Standard output is empty