JensAyton

// Yes, this is reduced from code that works and does something arguably useful.

protocol P1 {
    associatedtype A1
    func f(_: A1)
}

protocol P2: P1 {
    associatedtype A2: P2
    var a2: A2 { get }

JensAyton

Pre-pitch: Capturing cases as closures

Ever since key paths were introduced, giving us a tool to abstract over members of structs and enums, I have felt that there should be an equivalent tool for enums – particularly enums with associated values. I’ve been assuming this would take a similar form to key paths, but another approach recently occurred to me.

Let’s start with a motivating example: event handling. If you used Swift for Mac or Windows application development in the 90s, your code would have contained something like this:

// AppController.swift

func handleEvent(_ event: Event) {

JensAyton

import Foundation

public struct AnyEquatable: Equatable {
    private struct EquatableBox<T: Equatable>: Hashable {
        let value: T

        func hash(into hasher: inout Hasher) {
            preconditionFailure("EquatableBox must never be hashed")
        }
    }

JensAyton

enum Tristate: ExpressibleByNilLiteral, ExpressibleByBooleanLiteral {
    case maybe
    case no
    case yes

    init(nilLiteral: Void) {
        self = .maybe
    }

    init(booleanLiteral value: Bool) {

JensAyton

struct Test {}

extension Test: LosslessStringConvertible {
    init?(_ description: String) {
        print("unlabelled init")
    }

    var description: String { "Test" }
}

JensAyton

let opIncr: UInt8 = 43   // +
let opDecr: UInt8 = 45   // -
let opPrev: UInt8 = 60   // <
let opNext: UInt8 = 62   // >
let opFwd: UInt8 = 91    // [
let opBck: UInt8 = 93    // ]
let opOutput: UInt8 = 46 // .
let opInput: UInt8 = 44  // ,
let opStop: UInt8 = 0

JensAyton

extern "C" {
	// This is global, but you can call it what you like
	inline void MyPrefixedCFShow(const void *object) {
		// Redeclared system function is local scope and counts as extern "C"
		extern void CFShow(const void * object);
		CFShow(object);
	}
}

class DumbThing {

JensAyton

struct ifparams {
#if __has_feature(objc_arc)
	__unsafe_unretained
#endif
	dispatch_block_t then, otherwise;
};

static inline void iff(bool condition, struct ifparams params) {
	((condition?params.then:params.otherwise)?:^{})();
}

JensAyton

#ifndef format_h
#define format_h


#define reset   "0"
#define bold    "1"
#define red     "31"

#define format(first, ...) \
	"\e[" first join_format_codes(__VA_ARGS__) "m"

JensAyton

import Foundation


// Because the real thing crashes
enum Result {
	case Value(Any)
	case Error(NSError?)
}