ios - Swift: Why does switching over textfields work? -

for example:

func textfielddidbeginediting(textfield: uitextfield) {     switch textfield {     case statefield:         print("editing state")     case countryfield:         print("editing country")     default:         break     } } 

is because looking @ address fields? right way use switch statement?

under hood, switch statement uses pattern matching operator (~=) in order define comparisons can do. in case, it's using this version:

@warn_unused_result public func ~=<t : equatable>(a: t, b: t) -> bool 

this takes 2 equatable arguments of same concrete type. in switch statement, each case passed a, , statement switch on passed b. bool returns defines whether case should triggered, in case return value of a == b.

uitextfield inherits nsobject, conforms equatable via isequal. therefore valid use 2 uitextfields operator, , therefore valid use them in switch.

as base implementation, isequal checks pointer equality. therefore switch statement indeed checking given uitextfield exact same instance given case.

you think doing this:

if textfield == statefield {     print("editing state") } else if textfield == countryfield {     print("editing country") } else {     // 'default' case } 

which doing (in case of nsobject inherited classes):

if textfield.isequal(statefield)  {     print("editing state") } else if textfield.isequal(countryfield) {     print("editing country") } else {     // 'default' case } 

using switch here great usage – makes code clearer chaining lots of if & else if statements together.