如何在Swift 3中專門研究通用高階函數？

Question

我很快就將一些HTTP代碼組合在一起。 在測試類中，我具有以下功能：

func measureAsync<T>(_ block: @escaping ((Result<T>) -> Void) -> ()) {
    self.measure {
        let expect = self.expectation(description: "get from backend")
        block { (result) in
            expect.fulfill()
            XCTAssertNotNil(result.value, "value")
        }

        self.waitForExpectations(timeout: 10) { (error) in
            if let error = error {
                print("error", error)
            }
        }
    }
}

public func curry<A, B, C>(_ f : @escaping (A, B) -> C) -> (A) -> (B) -> C {
    return { (a : A) -> (B) -> C in
        { (b : B) -> C in
            f(a, b)
        }
    }
}

我試圖像這樣在測試用例中調用該函數：

    let block = curry(StorageClient.client.getProfilePicture)(URL.init(fileURLWithPath: "/User Photos/profile_MThumb.jpg"))
    measureAsync(block)

我得到了編譯器錯誤“無法將類型'((Result<UIImage>) -> Void) -> ()'為預期的參數類型'((Result<_>) -> Void) -> ()'

我該如何進行編譯？ 可能嗎？

Answer 1

我“解決”了。 這是一種hack。 但這確實起作用

func testProfilePicture() {
    let block = curry(StorageClient.client.getProfilePicture)(URL.init(fileURLWithPath: "/User Photos/profile_MThumb.jpg"))
    measureAsync(UIImage.self, block)
}

func measureAsync<T>(_ type: T.Type, _ block: Any) {
    self.measure {
        let expect = self.expectation(description: "get from backend")
        if let block = block as? (((Result<T>) -> Void) -> Void) {
            block { (result: Result<T>) in
                expect.fulfill()
                XCTAssertNotNil(result.value, "value is nil")
            }
        } else {
            fatalError("could not downcast block")
        }

        self.waitForExpectations(timeout: 10) { (error) in
            if let error = error {
                print("error", error)
            }
        }
    }
}