I see many users, but I don’t understand the benefits of Either. What is the difference between Eith...

# android

[lam bui]

I see many users, but I don’t understand the benefits of Either. What is the difference between Either and Pair in kotlin?
https://arrow-kt.io/docs/apidocs/arrow-core/arrow.core/-either/.

[David Rawson]

Probably more suited for the #arrow channel but I’ll give it a go 😛

Pair is a tuple with no info about what first and second mean. See “tuples obfuscate” in the Google Guava ideas graveyard:
https://github.com/google/guava/wiki/IdeaGraveyard

Either is an abstraction built for modelling the common scenario where an operation can succeed or fail, with failure represented by left and success represented by right. This can be an alternative to declaring functions that have a return type for success but rely on throwing exceptions to indicate failure.

Either provides functions like fold , flatMap etc. that allow chaining operations, and even a comprehension that allows writing imperative code in a block without using flatMap etc.

TL;DR Pair is very broad and Either is suited to a specific use case

[ephemient]

Pair always contains two values (one of each type), Either always contains one value (of either type). in PL/type theory terms, Pair<A, B> is A×B and Either<A, B> is A+B, which intuitively maps to the number of values they can take on

[lam bui]

that’s clear, thank you. Pair is product type, Either is Union.

[ephemient]

to be pedantic, it could be called a tagged union, since Either<A, A> contains more information than A | A. and Arrow's functions are very targeted towards using Either as an error-handling monad. but yes, exactly