[英]How to use type parameter in typealias?
I want to use a typealias for a function which is used in a generic class. 我想为泛型类中使用的函数使用类型别名。 One of the parameters of the function uses a generic type of the class. 函数的参数之一使用类的泛型类型。 This is a simplified example: 这是一个简化的示例:
class Bar {}
// no typealias - works
class TestGeneric<T: Bar> {
let myFunc: (T) -> String
init(myFunc: (T) -> String) {
self.myFunc = myFunc
}
}
let myFunc: (Bar) -> String = {(bar: Bar) in
return "hello"
}
let test = TestGeneric<Bar>(myFunc: myFunc)
println(test.myFunc(Bar()))
// typealias - doesn't compile
class TestTypealias<T: Bar> {
typealias MyFuncGeneric = (T) -> String
let myFunc: MyFuncGeneric
init(myFunc: MyFuncGeneric) {
self.myFunc = myFunc
}
}
let myFunc2: TestTypealias.MyFuncGeneric = {(bar: Bar) in
return "hello"
}
let test2 = TestTypealias<Bar>(myFunc: myFunc2) // Error: Cannot invoke initializer for type 'TestTypealias<Bar>' with an argument list of type '(myFunc: T -> String)'
println(test2.myFunc(Bar()))
Is there a way to solve this? 有办法解决吗? Or do I have to forgo typealias when using generics? 还是在使用泛型时必须放弃typealias? In the actual code I have a lot of parameters and really need a typealias... 在实际的代码中,我有很多参数,确实需要一个类型别名。
(Swift 1.2) (快速1.2)
This compiles and behaves as expected: 这将编译并按预期方式运行:
class Test< T >
{
typealias GenFunc = ( thing: T ) -> Void
let thing : T
init( thing: T )
{
self.thing = thing
}
func ExecuteFunc( genFunc: GenFunc )
{
genFunc( thing: self.thing )
}
}
Use: 采用:
let t = Test( thing: "blah" )
t.ExecuteFunc()
{ ( thing: String ) -> Void in
println( thing )
}
By writing 通过写
class TestGeneric<T: Bar>
all you've really done is to define T universally as being of type Bar when used inside of a method, so you can write this: 您真正要做的就是将T定义为在方法内部使用时的Bar类型,因此您可以这样编写:
func myFunc(aValue:T) {
}
instead of this: 代替这个:
func myFunc<T: Bar>(aValue:T) {
}
each time you want to define T as being of type Bar. 每次您想将T定义为Bar类型。
If you want the class itself to be generic you use only <T>
, for example: class TestGeneric<T>
and type is defined upon initializing. 如果希望类本身是泛型的,则仅使用<T>
,例如: class TestGeneric<T>
并且类型在初始化时定义。
class Bar {}
// no typealias - works
class TestGeneric<T> {
let myFunc: (T) -> String
init(myFunc: (T) -> String) {
self.myFunc = myFunc
}
}
let myFunc: Bar -> String = {(bar: Bar) in
return "hello"
}
let test = TestGeneric<Bar>(myFunc: myFunc)
println(test.myFunc(Bar()))
// typealias - doesn't compile
class TestTypealias<T> {
typealias MyFuncGeneric = T -> String
func myFunc(aValue:T) {
}
let myFunc: MyFuncGeneric
init(myFunc: MyFuncGeneric) {
self.myFunc = myFunc
}
}
let myFunc2: TestTypealias<Bar>.MyFuncGeneric = {(bar: Bar) in
return "hello"
}
let test2 = TestTypealias<Bar>(myFunc: myFunc2)
println(test2.myFunc(Bar()))
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