swift - Subscript Syntax to append values in array -


in swift programming language book explicitly states:

you can't use subscript syntax append new item end of array

the example provided in book states if replacement set of values has different length range replacing fine. example:

var shoppinglist = ["eggs", "milk", "chocolate"] shoppinglist[0...2] = ["bananas", "apples"] // shoppinglist = ["bananas", "apples"]

which makes sense because replacing 3 values values of banana , apple. however, if did instead:

var shoppinglist = ["eggs", "milk", "chocolate"] shoppinglist[0...2] = ["bananas", "apples", "sausage", "pear"] // shoppinglist = ["bananas", "apples", "sausage", "pear"]

i thought not allowed use subscript syntax append new item end of array, seems loophole in language. can explain me why happens and/if valid behaviour or bug? thanks!

when book says “you can’t use subscript syntax append new item end of array”, means is, “the way array.subscript (index: int) -> t has been implemented, can’t use append new item end of array”.

subscript bit of syntactic sugar function propertyish qualities takes arguments (in case index) , either gets or sets value (in case t). function, can whatever want. set value @ index, or fire nuclear missiles if wrote way.

as happens, array defines second overload subscript operates on ranges, , does have extending capabilities. book referring more conventional 1 takes single index.

to demonstrate, here’s extension array defines version of subscript, time 1 if name index extend:, extend array new value desired index:

extension array {     // add new subscript named argument     subscript (extending index: int) -> t {         { return self[index] }         set(newvalue) {             if index < self.endindex {                 self[index]             }             else {                 let extendby = index + 1 - self.endindex                 self.extend(repeat(count: extendby, repeatedvalue: newvalue))             }         }     } }  var = [1,2,3]  a[extending: 5] = 100 // [1, 2, 3, 100, 100, 100]

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