C++ High Performance

Receiving the type of a variable with decltype

The decltype keyword is used to retrieve the type of a variable and is used when an explicit type name is not available.

Sometimes, an explicit type name is not available, only the variable name is available. For example, polymorphic lambda functions (lambdas with auto as a parameter) do not name the type (as opposed to templated functions, where the type name has its own parameter):

Regular template function	Lambda function
Here, the type of v is visible as T: template <typename T> auto square_func(const T& v){ return v * v; }	Here, the type of v is not visible, as it is only denoted as auto: auto square_func_lbd=[](auto v){ return v * v; };

Take the previous sign function; if ...