106 lines
4.5 KiB
Swift
106 lines
4.5 KiB
Swift
// Copyright 2018 Google Inc. All rights reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at:
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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import Foundation
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public extension Promise {
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typealias Then<Result> = (Value) throws -> Result
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/// Creates a pending promise which eventually gets resolved with the same resolution as the
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/// promise returned from `work` block. The `work` block is executed asynchronously on the given
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/// `queue` only when `self` is fulfilled. If `self` is rejected, the returned promise is also
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/// rejected with the same error.
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/// - parameters:
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/// - queue: A queue to invoke the `work` block on.
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/// - work: A block to handle the value that `self` was fulfilled with.
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/// - returns: A new pending promise to be resolved with the same resolution as the promise
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/// returned from the `work` block.
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@discardableResult
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func then<Result>(
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on queue: DispatchQueue = .promises,
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_ work: @escaping Then<Promise<Result>>
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) -> Promise<Result> {
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let promise = Promise<Result>(objCPromise.__onQueue(queue, then: { objCValue in
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guard let value = Promise<Value>.asValue(objCValue) else {
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preconditionFailure("Cannot cast \(type(of: objCValue)) to \(Value.self)")
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}
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do {
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return try work(value).objCPromise
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} catch let error {
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return error as NSError
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}
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}))
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// Keep Swift wrapper alive for chained promise until `ObjCPromise` counterpart is resolved.
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objCPromise.__addPendingObject(promise)
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return promise
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}
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/// Creates a pending promise which eventually gets resolved with the value returned from `work`
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/// block. The `work` block is executed asynchronously on the given `queue` only when `self` is
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/// fulfilled. If `self` is rejected, the returned promise is also rejected with the same error.
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/// - parameters:
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/// - queue: A queue to invoke the `work` block on.
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/// - work: A block to handle the value that `self` was fulfilled with.
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/// - returns: A new pending promise to be resolved with the value returned from the `work` block.
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@discardableResult
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func then<Result>(
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on queue: DispatchQueue = .promises,
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_ work: @escaping Then<Result>
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) -> Promise<Result> {
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let promise = Promise<Result>(objCPromise.__onQueue(queue, then: { objCValue in
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guard let value = Promise<Value>.asValue(objCValue) else {
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preconditionFailure("Cannot cast \(type(of: objCValue)) to \(Value.self)")
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}
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do {
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let value = try work(value)
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return type(of: value) is NSError.Type
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? value as! NSError : Promise<Result>.asAnyObject(value)
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} catch let error {
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return error as NSError
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}
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}))
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// Keep Swift wrapper alive for chained promise until `ObjCPromise` counterpart is resolved.
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objCPromise.__addPendingObject(promise)
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return promise
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}
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/// Creates a pending promise which eventually gets resolved with the same resolution as `self`.
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/// `work` block is executed asynchronously on the given `queue` only when `self` is fulfilled.
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/// If `self` is rejected, the returned promise is also rejected with the same error.
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/// - parameters:
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/// - queue: A queue to invoke the `work` block on.
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/// - work: A block to handle the value that `self` was fulfilled with.
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/// - returns: A new pending promise to be resolved with the value passed into the `work` block.
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@discardableResult
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func then(
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on queue: DispatchQueue = .promises,
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_ work: @escaping Then<Void>
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) -> Promise {
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let promise = Promise(objCPromise.__onQueue(queue, then: { objCValue in
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guard let value = Promise<Value>.asValue(objCValue) else {
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preconditionFailure("Cannot cast \(type(of: objCValue)) to \(Value.self)")
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}
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do {
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try work(value)
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return Promise<Value>.asAnyObject(value)
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} catch let error {
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return error as NSError
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}
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}))
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// Keep Swift wrapper alive for chained promise until `ObjCPromise` counterpart is resolved.
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objCPromise.__addPendingObject(promise)
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return promise
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}
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}
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