Generic lambdas were introduced in C++14, where auto was used as a function parameter.
| C++14 |
|---|
// lambda definition
auto addTwo = [](auto first, auto second)
{
return first + second;
}; |
In C++20, similarly to how auto was used in lambdas, auto can now be used as a function parameter to get a function template.
C++20 has added abbreviated function templates, used to shorten the template version of the function.
| C++ | C++20 |
|---|---|
template< typename T >
T addTwo(T first, T second)
{
return first + second;
} |
// this is a template, without the word 'template'!
auto addTwo(auto first, auto second)
{
return first + second;
} |
(To be clear - it is the auto used as a param - even just one of the params - that makes it a template.)
Looking at it from the point of view of Concepts, auto acts like the most unconstrained Concept.