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257 lines
9.5 KiB
Swift
257 lines
9.5 KiB
Swift
import Dispatch
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/// Provides `catch` and `recover` to your object that conforms to `Thenable`
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public protocol CatchMixin: Thenable
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{}
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public extension CatchMixin {
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/**
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The provided closure executes when this promise rejects.
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Rejecting a promise cascades: rejecting all subsequent promises (unless
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recover is invoked) thus you will typically place your catch at the end
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of a chain. Often utility promises will not have a catch, instead
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delegating the error handling to the caller.
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- Parameter on: The queue to which the provided closure dispatches.
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- Parameter policy: The default policy does not execute your handler for cancellation errors.
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- Parameter execute: The handler to execute if this promise is rejected.
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- Returns: A promise finalizer.
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- SeeAlso: [Cancellation](https://github.com/mxcl/PromiseKit/blob/master/Documentation/CommonPatterns.md#cancellation)
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*/
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@discardableResult
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func `catch`(on: DispatchQueue? = conf.Q.return, flags: DispatchWorkItemFlags? = nil, policy: CatchPolicy = conf.catchPolicy, _ body: @escaping(Error) -> Void) -> PMKFinalizer {
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let finalizer = PMKFinalizer()
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pipe {
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switch $0 {
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case .rejected(let error):
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guard policy == .allErrors || !error.isCancelled else {
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fallthrough
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}
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on.async(flags: flags) {
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body(error)
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finalizer.pending.resolve(())
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}
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case .fulfilled:
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finalizer.pending.resolve(())
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}
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}
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return finalizer
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}
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}
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public class PMKFinalizer {
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let pending = Guarantee<Void>.pending()
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/// `finally` is the same as `ensure`, but it is not chainable
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public func finally(on: DispatchQueue? = conf.Q.return, flags: DispatchWorkItemFlags? = nil, _ body: @escaping () -> Void) {
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pending.guarantee.done(on: on, flags: flags) {
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body()
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}
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}
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}
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public extension CatchMixin {
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/**
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The provided closure executes when this promise rejects.
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Unlike `catch`, `recover` continues the chain.
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Use `recover` in circumstances where recovering the chain from certain errors is a possibility. For example:
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firstly {
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CLLocationManager.requestLocation()
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}.recover { error in
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guard error == CLError.unknownLocation else { throw error }
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return .value(CLLocation.chicago)
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}
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- Parameter on: The queue to which the provided closure dispatches.
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- Parameter body: The handler to execute if this promise is rejected.
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- SeeAlso: [Cancellation](https://github.com/mxcl/PromiseKit/blob/master/Documentation/CommonPatterns.md#cancellation)
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*/
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func recover<U: Thenable>(on: DispatchQueue? = conf.Q.map, flags: DispatchWorkItemFlags? = nil, policy: CatchPolicy = conf.catchPolicy, _ body: @escaping(Error) throws -> U) -> Promise<T> where U.T == T {
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let rp = Promise<U.T>(.pending)
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pipe {
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switch $0 {
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case .fulfilled(let value):
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rp.box.seal(.fulfilled(value))
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case .rejected(let error):
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if policy == .allErrors || !error.isCancelled {
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on.async(flags: flags) {
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do {
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let rv = try body(error)
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guard rv !== rp else { throw PMKError.returnedSelf }
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rv.pipe(to: rp.box.seal)
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} catch {
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rp.box.seal(.rejected(error))
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}
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}
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} else {
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rp.box.seal(.rejected(error))
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}
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}
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}
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return rp
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}
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/**
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The provided closure executes when this promise rejects.
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This variant of `recover` requires the handler to return a Guarantee, thus it returns a Guarantee itself and your closure cannot `throw`.
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- Note it is logically impossible for this to take a `catchPolicy`, thus `allErrors` are handled.
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- Parameter on: The queue to which the provided closure dispatches.
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- Parameter body: The handler to execute if this promise is rejected.
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- SeeAlso: [Cancellation](https://github.com/mxcl/PromiseKit/blob/master/Documentation/CommonPatterns.md#cancellation)
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*/
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@discardableResult
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func recover(on: DispatchQueue? = conf.Q.map, flags: DispatchWorkItemFlags? = nil, _ body: @escaping(Error) -> Guarantee<T>) -> Guarantee<T> {
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let rg = Guarantee<T>(.pending)
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pipe {
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switch $0 {
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case .fulfilled(let value):
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rg.box.seal(value)
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case .rejected(let error):
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on.async(flags: flags) {
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body(error).pipe(to: rg.box.seal)
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}
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}
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}
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return rg
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}
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/**
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The provided closure executes when this promise resolves, whether it rejects or not.
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firstly {
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UIApplication.shared.networkActivityIndicatorVisible = true
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}.done {
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//…
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}.ensure {
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UIApplication.shared.networkActivityIndicatorVisible = false
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}.catch {
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//…
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}
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- Parameter on: The queue to which the provided closure dispatches.
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- Parameter body: The closure that executes when this promise resolves.
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- Returns: A new promise, resolved with this promise’s resolution.
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*/
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func ensure(on: DispatchQueue? = conf.Q.return, flags: DispatchWorkItemFlags? = nil, _ body: @escaping () -> Void) -> Promise<T> {
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let rp = Promise<T>(.pending)
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pipe { result in
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on.async(flags: flags) {
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body()
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rp.box.seal(result)
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}
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}
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return rp
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}
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/**
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The provided closure executes when this promise resolves, whether it rejects or not.
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The chain waits on the returned `Guarantee<Void>`.
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firstly {
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setup()
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}.done {
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//…
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}.ensureThen {
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teardown() // -> Guarante<Void>
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}.catch {
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//…
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}
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- Parameter on: The queue to which the provided closure dispatches.
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- Parameter body: The closure that executes when this promise resolves.
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- Returns: A new promise, resolved with this promise’s resolution.
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*/
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func ensureThen(on: DispatchQueue? = conf.Q.return, flags: DispatchWorkItemFlags? = nil, _ body: @escaping () -> Guarantee<Void>) -> Promise<T> {
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let rp = Promise<T>(.pending)
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pipe { result in
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on.async(flags: flags) {
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body().done {
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rp.box.seal(result)
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}
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}
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}
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return rp
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}
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/**
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Consumes the Swift unused-result warning.
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- Note: You should `catch`, but in situations where you know you don’t need a `catch`, `cauterize` makes your intentions clear.
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*/
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@discardableResult
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func cauterize() -> PMKFinalizer {
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return self.catch {
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conf.logHandler(.cauterized($0))
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}
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}
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}
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public extension CatchMixin where T == Void {
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/**
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The provided closure executes when this promise rejects.
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This variant of `recover` is specialized for `Void` promises and de-errors your chain returning a `Guarantee`, thus you cannot `throw` and you must handle all errors including cancellation.
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- Parameter on: The queue to which the provided closure dispatches.
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- Parameter body: The handler to execute if this promise is rejected.
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- SeeAlso: [Cancellation](https://github.com/mxcl/PromiseKit/blob/master/Documentation/CommonPatterns.md#cancellation)
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*/
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@discardableResult
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func recover(on: DispatchQueue? = conf.Q.map, flags: DispatchWorkItemFlags? = nil, _ body: @escaping(Error) -> Void) -> Guarantee<Void> {
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let rg = Guarantee<Void>(.pending)
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pipe {
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switch $0 {
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case .fulfilled:
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rg.box.seal(())
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case .rejected(let error):
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on.async(flags: flags) {
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body(error)
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rg.box.seal(())
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}
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}
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}
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return rg
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}
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/**
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The provided closure executes when this promise rejects.
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This variant of `recover` ensures that no error is thrown from the handler and allows specifying a catch policy.
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- Parameter on: The queue to which the provided closure dispatches.
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- Parameter body: The handler to execute if this promise is rejected.
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- SeeAlso: [Cancellation](https://github.com/mxcl/PromiseKit/blob/master/Documentation/CommonPatterns.md#cancellation)
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*/
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func recover(on: DispatchQueue? = conf.Q.map, flags: DispatchWorkItemFlags? = nil, policy: CatchPolicy = conf.catchPolicy, _ body: @escaping(Error) throws -> Void) -> Promise<Void> {
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let rg = Promise<Void>(.pending)
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pipe {
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switch $0 {
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case .fulfilled:
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rg.box.seal(.fulfilled(()))
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case .rejected(let error):
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if policy == .allErrors || !error.isCancelled {
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on.async(flags: flags) {
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do {
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rg.box.seal(.fulfilled(try body(error)))
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} catch {
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rg.box.seal(.rejected(error))
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}
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}
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} else {
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rg.box.seal(.rejected(error))
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}
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}
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}
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return rg
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}
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}
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