Functions that can be deduced by their type signature

Question

I was introduced to this idea informally by this c++ talk Ben Deane “Using Types Effectively"

For example:

template<typename T, typename U>
T f(pair<T, U>);

can be deduced to be first.

• What is the proper terminology for this?
• Are there some resources to learn more?

Answer 1

David Young already answered this in the comments of my other question.

Regarding functions with only one possible implementation: This is the result of something called "parametricity". Sometimes it is not only one implementation, but the collection of possible implementations is very restricted. This fact is expressed by a "free theorem." Every parametrically polymorphic function has an associated free theorem. Some resources: 1, 2, 3, 4