Parameters Values: Default or Optional

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When we design function or API, have to choose parameters default values. Here are 3 common styles.

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enum UserType: String {
    case Weixin = "wechat"
    case Weibo = "weibo"
    case QQ = "qq"
}

// 1. Like NSLayoutAnchor, call function can be like less input parameters
func testDefaultParametersValue(userType: UserType = .Weibo) {
    print(userType)
}


testDefaultParametersValue()
testDefaultParametersValue(.QQ)

// 2. All parameters have to input
func testOptionalParametersValue(var userType: UserType?) {
    // Can set default value inside too
    if userType == nil {
        userType = .Weibo
    }
    
    print(userType)
}

testOptionalParametersValue(nil)
testOptionalParametersValue(.Weixin)


// 3. Like Kingfisher can less parameters or pass nil
func testAll(id: Int? = nil, city: String) {
    print(id)
    print(city)
}

testAll(city: "Shanghai")
testAll(nil, city: "Shanghai")
testAll(12, city: "Shanghai")