字典重载

由于目前没有简单的方法在 Swift 中组合字典，因此重载 +和+= 运算符以使用泛型添加此功能会很有用。

// Combines two dictionaries together. If both dictionaries contain
// the same key, the value of the right hand side dictionary is used.
func +<K, V>(lhs: [K : V], rhs: [K : V]) -> [K : V] {
    var combined = lhs
    for (key, value) in rhs {
        combined[key] = value
    }
    return combined
}

// The mutable variant of the + overload, allowing a dictionary
// to be appended to 'in-place'.
func +=<K, V>(inout lhs: [K : V], rhs: [K : V]) {
    for (key, value) in rhs {
        lhs[key] = value
    }
}

Version >= 3.0

从 Swift 3 开始，inout 应该放在参数类型之前。

func +=<K, V>(lhs: inout [K : V], rhs: [K : V]) { ... } 

用法示例：

let firstDict = ["hello" : "world"]
let secondDict = ["world" : "hello"]
var thirdDict = firstDict + secondDict // ["hello": "world", "world": "hello"]

thirdDict += ["hello":"bar", "baz":"qux"] // ["hello": "bar", "baz": "qux", "world": "hello"]