Templates are a feature of the C++ programming language that allows functions and classes to operate with generic types.
For this reason, classes employing templated methods place the implementation in the headers (*.h files) as no symbol could be compiled without knowing the type beforehand.
The format for declaring function templates with type parameters is: Both expressions have the same meaning and behave in exactly the same way.
The latter form was introduced to avoid confusion,[3] since a type parameter need not be a class until C++20.
For example, the C++ Standard Library contains the function template max(x, y) which returns the larger of x and y.
[citation needed] The compiler output will be identical to what would have been produced if the source code had contained two separate non-templated versions of max(), one written to handle int and one written to handle double.
In the third case automatic deduction of max(3, 7.0) would fail because the type of the parameters must in general match the template arguments exactly.
This function template can be instantiated with any copy-constructible type for which the expression y < x is valid.
For example, the template definition below defines a specific implementation of max() for arguments of type const char*: C++11 introduced variadic templates, which can take a variable number of arguments in a manner somewhat similar to variadic functions such as std::printf.
However, the arrival in C++11 of standard library features such as std::conditional has provided another, more flexible way to handle conditional template instantiation.