CustomStringConvertible

custom-stirng-convertible.swift

struct Position {
    var x: Int = 0
    var y: Int = 0
    
    func string() -> String {
        return "(\(x), \(y))"
    }
}

// CustomStringConvertible provides "description" property. 
// Before Xcode 7 beta 3 it was called "Printable" protocol.
// Using this protocol it cause that printing object under 
// debugger will gives better description by default.

struct Position: CustomStringConvertible {
    var x = 0
    var y = 0
    
    var description: String {
        return "(\(x), \(y))"
    }
}

Hi. I am trying to look for clues as to how the computed property description is being called.

For example, using your code, I attempt to print the reference to the structure that I've created:

struct Position: CustomStringConvertible {
    var x = 0
    var y = 0
    
    var description: String {
        return "(\(x), \(y))"
    }
}

let position = Position()
print(position) // This should print "0, 0"

I'm just curious, how is the computed property description (implicitly) called?

Just to note, if I attempt the same on the structure that doesn't conform to the CustomStringConvertible protocol, the output is:
Position(x: 0, y: 0)