Documentation/history of unapplied method references

theisegeberg · September 21, 2023, 5:09pm

I'm curious about unapplied method references. I might have the name wrong, and that's why I can't find very much information (I've found a little nooks and crannies).

I'm interested in any historic facts and references to any documentation or articles.

Example of an unapplied method reference:

let unappliedMethodReference:(String) -> () -> String = String.lowercased

I'm interested because I'm working on a SwiftUI pattern that leverages this. E.g. Text.foregroundColor as an input to a SwiftUI View.

Many thanks for sharing your wisdom.

jrose · September 21, 2023, 5:28pm

github.com

apple/swift-evolution/blob/main/proposals/0042-flatten-method-types.md

# Flattening the function type of unapplied method references

* Proposal: [SE-0042](0042-flatten-method-types.md)
* Author: [Joe Groff](https://github.com/jckarter)
* Review Manager: [Chris Lattner](https://github.com/lattner)
* Status: **Rejected**
* Decision Notes: [Original acceptance](https://forums.swift.org/t/accepted-se-0042-flattening-the-function-type-of-unapplied-method-references/1926). The proposal was not implemented in time for Swift 3, and is now source-breaking.
  
* Bug: [SR-1051](https://bugs.swift.org/browse/SR-1051)

## Introduction

An **unapplied method reference**, such as `Type.instanceMethod` in the
following example, currently produces a curried function value of type
`(Self) -> (Args...) -> Ret`:

```swift
struct Type {
  var x: Int
  func instanceMethod(y y: Int) -> Int {

This file has been truncated. show original

And a bit more from me, when that was never implemented:

Nobody1707 · September 21, 2023, 6:55pm

It'd be so nice if we could get uncurried unnaplied references in Swift 6. It probably won't happen, but it'd be great. let mutableFunc = b.someMutableMethod having the type (inout B) -> () -> Void was never a good idea.

theisegeberg · September 21, 2023, 7:20pm

Do any of you know the origins of this implementation? Does it have some history in ObjC?