Cannot convert value of type 'Foo!' to expected argument type 'Foo!'

问题

I'm baffled by something I've run into a couple of times. I sometimes get errors similar to the following

Cannot convert value of type 'Foo!' to expected argument type 'Foo!

I've searched SO, but haven't really found anything that explains why Foo! isn't the same as Foo!.

Here's an example:

// FooViewModel.swift
class FooViewModel: BaseViewModel {
    fileprivate var foo: Foo!
    fileprivate var bar: Bar = Bar()

    init!(model: Foo!) {
        super.init()
        foo = model
    }

    override init() {
        super.init()
    }

    func setFooModel(_ model: Foo!) {
        self.foo = model
    }

    func getFooModel() -> Foo! {
        return self.foo
    }

    func getBar() -> Bar {
        return bar
    }

    func getBlah() -> String {
        return "Blah"
    }
}

Here is the unit test that generates the error:

import XCTest
@testable import WooHoo

class FooViewModelTests: XCTestCase {

    override func setUp() {
        super.setUp()
    }

    override func tearDown() {
        super.tearDown()
    }

    func testGetBar() {
        var foo = Foo()
        let vm = FooViewModel()

        // The following line generates the error
        vm.setFooModel(foo)

        XCTAssertEqual("Tell us your Foo for the Bar program.", vm.getBlah())
    }
}

I've tried a number of variations for vm.setFooModel(foo) to no avail, e.g. vm.setFooModel(foo!) or declaring foo as var foo: Foo! = Foo().

edit: Note that the code above is for illustrating the issue I'm running into and is not the operational code.

回答1:

I figured this out. My view model was part of the tests target. After I set it to the run target only, the issue resolved. FYI.

来源：https://stackoverflow.com/questions/46167309/cannot-convert-value-of-type-foo-to-expected-argument-type-foo

标签

swift

xctest