Open Radar

 
F# provides a standard binary operator |>, the "pipe-forward" operator, which applies the function on its right-hand side to the value on its left-hand side. The operator can be defined in Swift like this:

    operator infix |> { associativity left }
    func |> <T,U>(lhs : T, rhs : T -> U) -> U {
        return rhs(lhs);
    }

This operator provides benefits both in readability and in IDE autocompletion support. For example, one can write an expression like this:

    let rows = resultCollection |>  filterBy(selectedCityName) |> orderBy(selectedColumn)

instead of in traditional inside-out/right-to-left function application notation, which would be this:

    let rows = orderBy(selectedColumn)(filterBy(selectedCityName)(resultCollection))

The left-to-right version would be more readable to most people.

When the user types the argument first, and then the |> operator, Xcode could then determine which functions are available that can be applied to an argument of that type and provide an appropriate autocompletion list. This is helpful.

This operator was created for F#, but is also in the Ocaml Batteries Included library and used elsewhere. If Swift provides such an operator, it would be nice to use the same notation used in other languages.

See https://gist.github.com/kristopherjohnson/ed97acf0bbe0013df8af for additional examples and commentary.