58 lines
2.0 KiB
Swift
58 lines
2.0 KiB
Swift
/// Used to lazily set context data. Useful for example if you have some data that requires heavy calculations, and may
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/// not be used in every render possiblity.
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public final class LazyValueWrapper {
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private let closure: (Context) throws -> Any
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private let context: Context?
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private var cachedValue: Any?
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/// Create a wrapper that'll use a **reference** to the current context.
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/// This means when the closure is evaluated, it'll use the **active** context at that moment.
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///
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/// - Parameters:
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/// - closure: The closure to lazily evaluate
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public init(closure: @escaping (Context) throws -> Any) {
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self.context = nil
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self.closure = closure
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}
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/// Create a wrapper that'll create a **copy** of the current context.
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/// This means when the closure is evaluated, it'll use the context **as it was** when this wrapper was created.
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///
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/// - Parameters:
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/// - context: The context to use during evaluation
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/// - closure: The closure to lazily evaluate
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/// - Note: This will use more memory than the other `init` as it needs to keep a copy of the full context around.
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public init(copying context: Context, closure: @escaping (Context) throws -> Any) {
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self.context = Context(dictionaries: context.dictionaries, environment: context.environment)
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self.closure = closure
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}
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/// Shortcut for creating a lazy wrapper when you don't need access to the Stencil context.
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///
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/// - Parameters:
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/// - closure: The closure to lazily evaluate
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public init(_ closure: @autoclosure @escaping () throws -> Any) {
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self.context = nil
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self.closure = { _ in try closure() }
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}
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}
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extension LazyValueWrapper {
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func value(context: Context) throws -> Any {
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if let value = cachedValue {
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return value
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} else {
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let value = try closure(self.context ?? context)
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cachedValue = value
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return value
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}
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}
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}
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extension LazyValueWrapper: Resolvable {
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public func resolve(_ context: Context) throws -> Any? {
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let value = try self.value(context: context)
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return try (value as? Resolvable)?.resolve(context) ?? value
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}
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}
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