What is the difference between using a struct with two fields and a pair?

std::pair provides pre-written constructors and comparison operators. This also allows them to be stored in containers like std::map without you needing to write, for example, the copy constructor or strict weak ordering via operator < (such as required by std::map). If you don’t write them you can’t make a mistake (remember how strict weak ordering works?) so it’s more reliable just to use std::pair.

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