CODEWITHSUNDEEP
arraysswiftgenerics
Dustin Jia
Dustin Jia

Reputation: 67

cannot invoke 'append' with an argument list of type '(T)'

Just got this strange error when trying to write a stack with generic type in latest playground. I really don't understand what's wrong here, can someone explain to me why I got this error? 

class MyStack<T> {
    var stack1 = [T]()

    func push<T>(value: T) {
        stack1.append(value)  // Error: cannot invoke 'append' with an argument list of type '(T)'
    }
}

Upvotes: 0

Views: 981

Answers (1)

tomahh
tomahh

Reputation: 13661

The class is already generic, no need to make push generic too

class MyStack<T> {
    var stack1 = [T]()

    func push(value: T) {
        stack1.append(value)
    }
}

When push is declared as push<T>, the generic parameter overrides the one defined on the class. So, if we were to rename the generic parameters, we'd get

class MyStack<T1> {
    var stack1 = [T1]()

    func push<T2>(value: T2) {
        stack1.append(value)  // Error: cannot invoke 'append' with an argument list of type '(T2)'
    }
}

presented like this, it makes sense that we cannot push a T2 in [T1].

Upvotes: 2

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