swift - What the difference between function and subscript, particularly in below code? -

i read "the swift programming language" , subscript make me confused, there's example below subscript, implement function, subscript mean compared function?

there same output "6 times 3 18" below example.

struct timestable {     let multiplier: int     subscript(index: int) -> int {         return multiplier * index     } }  let threetimestable = timestable(multiplier: 3)  println("6 times 3 \(threetimestable[6])")   struct timestable2 {     let multiplier: int     func times (index: int) -> int {         return multiplier * index     } }  let threetimestable2 = timestable2(multiplier: 3)  println("6 times 3 \(threetimestable2.times(6))") 

subscripts subset of functions. can't quite things function can (they can't take inout parameters, instance), other things well, convenient syntax (the square brackets [ ]).

they used retrieve item collection index. instead of having write,

let array = [7, 3, 6, 8] let x = array.itematindex(0)   // x == 7 

we can write,

let x = array[0] 

or instead of,

let dictionary = ["one": 1, "two": 2] let x = dictionary.objectforkey("one")  // x == optional(1) 

we can write,

let x = dictionary["one"]  // x == optional(1) 

the syntax short , intuitive. , okapi said, can act getters , setters variable properties, computed property.

the example in documentation non-traditional use of subscripts. think supposed illustrate point making - subscripts can used in place of function or computed property anywhere think [bracket] syntax convenient , useful. use not limited accessing items in collection.

you refine own syntactic sugar.