create a generic struct in swift

To create a generic struct in Swift, you need to use type parameters. Type parameters are placeholders for types that will be specified when the struct is used. Here's an example of a simple generic struct that uses a type parameter:

main.swift
struct MyStack<T> {
    private var elements = [T]()
    
    mutating func push(_ element: T) {
        elements.append(element)
    }
    
    mutating func pop() -> T? {
        return elements.popLast()
    }
}
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In this example, the MyStack struct has a type parameter T. This means that when you use MyStack, you can specify what type to use for T. For example, you could create a stack of strings like this:

main.swift
var stack = MyStack<String>()
stack.push("hello")
stack.push("world")
print(stack.pop()) // prints "world"
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The MyStack struct also demonstrates type constraints. In this case, the push method of the struct requires that the element being pushed is of type T by specifying the type parameter T after the function name. Similarly, the pop method returns an optional value of type T.

You can use type constraints to specify that the type parameter should conform to certain protocols. For example, if you only want to allow types that can be added together, you can add the Numeric protocol as a type constraint:

main.swift
struct MyAddition<T: Numeric> {
    func add(_ a: T, _ b: T) -> T {
        return a + b
    }
}
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Now you can use the MyAddition struct to add together any types that conform to Numeric, such as integers or floating-point numbers:

main.swift
let adder = MyAddition<Int>()
print(adder.add(2, 3)) // prints "5"
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