Swift：将函子传递给函子称为传递的函子

Question

How do I pass a function into another function without causing the passed in function to get called the moment it is read as an argument?

Here is an example of one function getting called simply by being an argument.

func second() {
    print("second")
}

func first(_: ()) {
    print("first")
}

first(second())

-------console output--------
second
first

I want to pass second into first so that I can call second() somewhere inside of first's body, but as you can see, second gets called immediately simply by being an argument.

Answer 1

func first(_: ()) {
    print("first")
}

This is a function that takes a Void as its argument (and ignores it). Void is a typealias for the empty tuple () . You meant:

func first(f: () -> Void) {}

That is a function that takes a function that returns nothing (and calls its parameter f rather than ignoring it).

first(second())

This calls second and then passes the result to first . You meant:

first(second)