JadenGeller

The Capability Environment Pattern

A compile-time dependency injection pattern for Rust with zero runtime cost.

The Problem

Services need other services:

impl OrderService {

JadenGeller

import Foundation

/// Represents a specific day in the Gregorian calendar as an integer offset.
///
/// `CalendarDay` provides a timezone-stable way to identify calendar days.
/// When created, it captures which Gregorian calendar day a date falls on
/// according to the specified timezone, then stores this as an integer offset
/// from Apple's reference date (January 1, 2001).
///
/// This type is useful when you need to:

JadenGeller

import SwiftUI

struct DateComponentsTimelineSchedule: TimelineSchedule {
    let components: DateComponents
    let calendar: Calendar
    let matchingPolicy: Calendar.MatchingPolicy
    
    init(
        components: DateComponents,
        calendar: Calendar = .current,

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struct OnChangeTask<T: Equatable>: ViewModifier {
    let value: T
    let action: () async -> Void
    @State private var updateCount = 0
    
    func body(content: Content) -> some View {
        content
            .onChange(of: value) {
                updateCount += 1
            }

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/// A view that displays a collection of items in a scrollable list that can "zoom" to focus on a single selected item.
///
/// `ZoomNavigator` provides a navigation pattern similar to the iOS lock screen wallpaper picker,
/// where items can be viewed together in a scrollable list or individually in full screen.
/// The same view instance is maintained during transitions, preserving state and identity.
///
/// When no item is selected (`selection` is `nil`), all items are displayed in a scrollable list.
/// When an item is selected, the view filters to show only that item, expanded to fill the available space.
struct ZoomNavigator<Data: RandomAccessCollection, ID: Hashable, Content: View, Background: View, Modifier: ViewModifier>: View {
    var data: Data

JadenGeller

The Service Linker Pattern

A way to thread dependencies through your app using Swift's protocol system.

The Problem

You have services that need other services:

struct OrderService {

JadenGeller

import SwiftUI

struct AttributedStringBuilder {
    @Stack var attributes: RichTextAttributes = .init()
    var string: AttributedString = ""
    
    mutating func text(_ span: String) {
        string += AttributedString(span, attributes: .init(attributes))
    }
    

JadenGeller

@propertyWrapper
struct Stack<Value> {
    private var history: [Value]

    init(wrappedValue initialValue: Value) {
        self.history = [initialValue]
    }

    var wrappedValue: Value {
        get { history[history.endIndex - 1] }

JadenGeller

Markdown Extensions

Component Directives

• Component Directive: A code block that defines a custom component.
• Info String: Starts with a $COMPONENT-NAME, which is @ followed by an $IDENTIFIER (e.g., @component-name).
• Front Matter: Enclosed within --- delimiters, specifies component attributes.
• Nesting: Use more backticks for the parent block than the child, respecting CommonMark.
• Content: Valid markdown, which may nest component directives.

Examples

JadenGeller

from itertools import zip_longest, chain
from dataclasses import dataclass, field

@dataclass
class Tree:
    value: any
    children: list = field(default_factory=list)
    
    def levels(self):
        yield [self]