In Swift, "block passing" refers to the concept of taking a block of code or closure as an argument and executing it later within a function.
Here's an example:
func performCalculation(_ a: Int, _ b: Int, using operation: (Int, Int) -> Int) -> Int {
return operation(a, b)
}
let addClosure = { (a: Int, b: Int) -> Int in
return a + b
}
let subtractClosure = { (a: Int, b: Int) -> Int in
return a - b
}
let result1 = performCalculation(3, 4, using: addClosure) // result1 = 7
let result2 = performCalculation(9, 2, using: subtractClosure) // result2 = 7
In the example above, we define a function performCalculation that takes two integer arguments a and b, and a closure operation that takes two integers and returns an integer. The function simply calls the operation closure with the given arguments and returns the result.
We then define two closures addClosure and subtractClosure that perform addition and subtraction operations, respectively. We use these closures as arguments to the performCalculation function and pass in the integers 3 and 4 (in the case of addClosure) and 9 and 2 (in the case of subtractClosure).
The function executes the passed-in closure with the given arguments and returns the result. In the case of addClosure, the result is 7 (since 3 + 4 = 7), while in the case of subtractClosure, the result is also 7 (since 9 - 2 = 7). This demonstrates how block passing can be used to pass different blocks of code to a function to achieve different results.