81 lines
3 KiB
Swift
81 lines
3 KiB
Swift
//
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// Preference.swift
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//
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// Copyright 2026 Brendan Szymanski <hello@bscubed.dev>
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//
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// This program is free software: you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program. If not, see <https://www.gnu.org/licenses/>.
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//
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// SPDX-License-Identifier: GPL-3.0-or-later
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//
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import LuminateCore
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import Portico
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/// Shared reference storage for a wrapper's mount-time slot resolution.
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@MainActor private final class ResolvedPreferences<Value: PreferenceValue> {
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var coordinator: Preferences?
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var slot: PreferenceSlot<Value>?
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}
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/// Reads and writes one persisted preference like Portico's `@State`.
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///
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/// A missing key reads as `nil` without a fallback. Reads inside reactive closure modifiers track the
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/// key, writes update every reader, and persistence is queued asynchronously off the main actor.
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@propertyWrapper @MainActor package struct Preference<Value: PreferenceValue>: DynamicProperty {
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private let key: PreferenceKey<Value>
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private let resolved = ResolvedPreferences<Value>()
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/// Creates a preference declaration for `key`.
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///
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/// - Parameter key: The stable typed preference identifier.
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package init(_ key: PreferenceKey<Value>) {
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self.key = key
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}
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/// Resolves the declaration against the mounting environment.
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///
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/// - Parameter environment: The environment supplied by the mounted view tree.
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package func _resolve(in environment: EnvironmentValues) {
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let preferences = environment.preferences
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if let previous = resolved.coordinator, previous !== preferences {
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fatalError(
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"@Preference: view instance mounted into two different environment scopes. "
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+ "A view instance resolves its preferences once; build a fresh instance per mount."
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)
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}
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resolved.coordinator = preferences
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resolved.slot = preferences.slot(for: key)
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}
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/// The current persisted value, or `nil` when the key is unset.
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package var wrappedValue: Value? {
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get { slot.value }
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nonmutating set { slot.value = newValue }
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}
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/// A live binding to the optional preference value.
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package var projectedValue: Binding<Value?> {
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Binding(slot, \PreferenceSlot<Value>.value)
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}
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/// The slot bound at mount.
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///
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/// Traps rather than inventing storage when read before `_resolve`.
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private var slot: PreferenceSlot<Value> {
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guard let slot = resolved.slot else {
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fatalError("@Preference read before its view was mounted.")
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}
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return slot
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}
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}
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