Defining Alias Templates
Learn to define alias templates.
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In C++, an alias is a name used to refer to a type that has been previously defined, whether a built-in type or a user-defined type. The primary purpose of aliases is to give shorter names to types that have a long name or provide semantically meaningful names for some types. This can be done either with a typedef declaration or with a using declaration (the latter was introduced in C++11). Here are several examples using typedef:
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typedef int index_t;typedef std::vector<std::pair<int, std::string>> NameValueList;typedef int (*fn_ptr)(int, char);template<typename T>struct foo{typedef T value_type;};
In this example, index_t is an alias for int, NameValueList is an alias for std::vector<std::pair<int, std::string>>, while fn_ptr ...