dabrahams

extension ObjectIdentifier {
  /// Returns true if the object identified by `self` is uniquely referenced.
  ///
  /// - Requires: the object identified by `self` exists.
  /// - Note: will only work when called from a mutating method
  internal func _liveObjectIsUniquelyReferenced() -> Bool {
    var me = self
    return withUnsafeMutablePointer(to: &me) {
      $0.withMemoryRebound(to: AnyObject.self, capacity: 1) {
        _isUnique(&$0.pointee)

anandabits

// This example shows how closed protocols can be emulated in Swift today.
// The technique leverages Swift's support for public (but not open) classes.

// First, it's worth observing that there is an almost trivial technique that can be used when
// it is possible to specify a (possibly abstract) superclass for all conforiming types.
// Simply declare a public (not open) base class and a protocol with a Self inheritance constraint.
// Swift does not support open subclasses of a public superclass so no classes outside the module
// will be able to meet the self inheritance constraint.
public class FooBase {}
public protocol Foo where Self: FooBase {}

tclementdev

libdispatch efficiency tips

The libdispatch is one of the most misused API due to the way it was presented to us when it was introduced and for many years after that, and due to the confusing documentation and API. This page is a compilation of important things to know if you're going to use this library. Many references are available at the end of this document pointing to comments from Apple's very own libdispatch maintainer (Pierre Habouzit).

My take-aways are:

• You should create very few, long-lived, well-defined queues. These queues should be seen as execution contexts in your program (gui, background work, ...) that benefit from executing in parallel. An important thing to note is that if these queues are all active at once, you will get as many threads running. In most apps, you probably do not need to create more than 3 or 4 queues.

• Go serial first, and as you find performance bottle necks, measure why, and if concurrency helps, apply with care, always validating under system pressure. Reuse

airspeedswift

/// Conform references types for use in the COW wrapper to this protocol
protocol Cowable: class {
  /// Make a new unique instance of `copied`
  static func makeUnique(_ copied: Self) -> Self
}

/// A wrapper that turns a Cowable reference type into a value-semantic
/// type with access to all of its properties
@dynamicMemberLookup

anandabits

/// - returns: `true` when dynamic type is `Equatable` and `==` returns `true`, otherwise `false`.
func areEquatablyEqual(_ lhs: Any, _ rhs: Any) -> Bool {
    func receiveLHS<LHS>(_ typedLHS: LHS) -> Bool {
        guard
            let rhsAsLHS = rhs as? LHS
            else { return false }
        return areEquatablyEqual(typedLHS, rhsAsLHS)
    }
    return _openExistential(lhs, do: receiveLHS)
}

anandabits

func testIsBidirectional() {
    func assert<C: Collection>(_ collection: C, isBidirectional: Bool) {
        XCTAssertEqual(collection.isBidirectional, isBidirectional)
    }

    assert([1, 2, 3], isBidirectional: true)
    assert(Set([1, 2, 3]), isBidirectional: false)
}

extension Collection {

dabrahams

protocol True {}
struct IsBidirectional<C> {}
extension IsBidirectional: True where C : BidirectionalCollection {  }
extension Collection {
  var isBidirectional: Bool {
    return IsBidirectional<Self>() is True
  }
}

func testIsBidirectional() {

magnuskahr

import SwiftUI

struct EnumPicker<T: Hashable & CaseIterable, V: View>: View {
    
    @Binding var selected: T
    var title: String? = nil
    
    let mapping: (T) -> V
    
    var body: some View {

skymobilebuilds

#!/bin/bash -e

echo "🤡 Applying carthage 12 and 13 workaround 🤡"

xcconfig=$(mktemp /tmp/static.xcconfig.XXXXXX)
# For Xcode 12 make sure EXCLUDED_ARCHS is set to arm architectures otherwise
# the build will fail on lipo due to duplicate architectures.
CURRENT_XCODE_VERSION=$(xcodebuild -version | grep "Build version" | cut -d' ' -f3)
echo 'EXCLUDED_ARCHS__EFFECTIVE_PLATFORM_SUFFIX_simulator__NATIVE_ARCH_64_BIT_x86_64__XCODE_1200 = arm64 arm64e armv7 armv7s armv6 armv8' > $xcconfig
echo "EXCLUDED_ARCHS__EFFECTIVE_PLATFORM_SUFFIX_simulator__NATIVE_ARCH_64_BIT_x86_64__XCODE_1200__BUILD_$CURRENT_XCODE_VERSION = arm64 arm64e armv7 armv7s armv6 armv8" >> $xcconfig

DougGregor