Swift generics and extensions need to workout -

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• array extension remove object value 13 answers

im learning swift currently. while learning i'm stuck generics. im solving 1 simple problem -> return index of specified element in array

import uikit  extension array {  func indexofletter<t:equatable>(item:t) -> int {     var = 0     (index, value) in enumerate(self)     {         if value == item         {             return         }         i++     }      return -1; } }   var arrayofitems = ["a","b"] arrayofitems.indexofletter("a") 

in code i'm getting error

can not compare 2 operands using == operator of type t.

the answer problem becomes more clear if use letter other t our generic identifier.

change method signature use letter u. , error message:

binary operator '==' cannot applied operands of type 't' , 'u'

this same error, it's made more clear using different letter. array type generic generic identifier t type.

when use u unmasks real problem.

the equatable protocol requires our type defines == comparisons itself. compare 2 u's long u's type equatable. equatable protocol not ensure can compare u t using ==.

this stack overflow answer can provide insight on difficulties of using equatable protocol generics.