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mayoff / ConversationView.swift
Created Feb 14, 2020
playground demonstrating SwiftUI PreferenceKey, EnvironmentKey, and GeometryReader
View ConversationView.swift
import SwiftUI
import PlaygroundSupport
struct EqualWidthKey: PreferenceKey {
static var defaultValue: CGFloat? { nil }
static func reduce(value: inout CGFloat?, nextValue: () -> CGFloat?) {
switch (value, nextValue()) {
case (_, nil): break
case (nil, let next): value = next
mayoff / SteppingSubscriber.swift
Created Dec 18, 2019
Custom Combine operator for stepping a publisher's signals through function
View SteppingSubscriber.swift
// See
import Combine
import Foundation
extension Publisher {
func step(with stepper: @escaping (SteppingSubscriber<Output, Failure>.Event) -> ()) -> AnyCancellable {
let subscriber = SteppingSubscriber<Output, Failure>(stepper: stepper)
return .init(subscriber)
mayoff / decode-dyn-uti.swift
Created Mar 14, 2019
Swift command-line script to decode dynamic UTIs
View decode-dyn-uti.swift
#!/usr/bin/xcrun swift
extension String {
static let bitsForCodeUnit: [Character: [UInt8]] = {
var dict = [Character: [UInt8]]()
for (i, ch) in "abcdefghkmnpqrstuvwxyz0123456789".enumerated() {
let bits = Array((0 ..< 5).map({ UInt8((i >> $0) & 1) }).reversed())
dict[ch] = bits
mayoff / unowned-safety-dance.swift
Created Feb 23, 2019
test Swift unowned safety
View unowned-safety-dance.swift
class MyObject { }
var o = MyObject()
print("strong o = \(o)")
unowned let u = o
print("unowned u = \(u)")
o = MyObject()
mayoff / main.m
Created Feb 11, 2019
Set pHYs chunk (DPI) of PNG
View main.m
@import AppKit;
@import ImageIO;
@import CoreServices;
#define fromCF (__bridge id)
#define toCF (__bridge CFTypeRef)
int main(int argc, const char * argv[]) {
@autoreleasepool {
CGRect rect = CGRectMake(0, 0, 100, 100);
mayoff / wedges-with-gaps.swift
Created Dec 27, 2018
Simon game wedges in iOS
View wedges-with-gaps.swift
import UIKit
import PlaygroundSupport
typealias Radians = CGFloat
extension UIBezierPath {
static func simonWedge(innerRadius: CGFloat, outerRadius: CGFloat, centerAngle: Radians, gap: CGFloat) -> UIBezierPath {
let innerAngle: Radians = CGFloat.pi / 4 - gap / (2 * innerRadius)
let outerAngle: Radians = CGFloat.pi / 4 - gap / (2 * outerRadius)
mayoff /
Created Oct 10, 2018
Decimal / NSDecimal support for lldb
# Decimal / NSDecimal support for lldb
# Put this file somewhere, e.g. ~/.../lldb/
# Then add this line to ~/.lldbinit:
# command script import ~/.../lldb/
import lldb
def stringForDecimal(sbValue, internal_dict):
from decimal import Decimal, getcontext
View Main.storyboard
<?xml version="1.0" encoding="UTF-8"?>
<document type="" version="3.0" toolsVersion="14313.18" targetRuntime="iOS.CocoaTouch" propertyAccessControl="none" useAutolayout="YES" useTraitCollections="YES" useSafeAreas="YES" colorMatched="YES" initialViewController="BYZ-38-t0r">
<device id="retina3_5" orientation="portrait">
<adaptation id="fullscreen"/>
<plugIn identifier="" version="14283.14"/>
<capability name="Safe area layout guides" minToolsVersion="9.0"/>
<capability name="documents saved in the Xcode 8 format" minToolsVersion="8.0"/>
mayoff / !
Last active Feb 11, 2020
Debugging Objective-C blocks in lldb
View !

The attached lldb command pblock command lets you peek inside an Objective-C block. It tries to tell you where to find the source code for the block, and the values captured by the block when it was created.

Consider this example program:

#import <Foundation/Foundation.h>

@interface Foo: NSObject

@implementation Foo
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