swift - Immutable `var` array -

i'd create array in swift immutable, can replaced, in style of functional programming.

i understand can create them in way:

var mutable   = [1,2,3] // can change reference, add, remove, etc let immutable = [4,5,6] // cannot replace reference or add, remove, etc 

i want properties of immutability, still able change immutable array variable points to. example, fail:

myarr.append(42) // fails. immutable array 

but succeed:

// desired behavior: // multiply each element in immutable array 2 // return new immutable array, assigned old var immutable = immutable.map { $0 * 2 } // error: can't replace immutable ref 

similar, not answers:

• ways make arrays , collections, not kind i'm asking about
• previous language issue made arrays partially mutable

what want doesn't make sense array, because value type value semantics. value of variable is array -- ability change variable , ability change array in way same thing.

semantically there no difference between:

myarr.append(42) 

and (made up):

myarr = myarr.newarraywithappending(42) 

in way, can imagine any "modification" value type variable implemented assigning new value variable. (it's not done way because inefficient, semantics point of view, there no reason why not implemented way.)

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the concept of "mutability" makes sense reference types, variable reference points actual object, , actual object can shared between multiple references (so "mutation" through 1 reference can seen through one).

with reference types, can want, example immutable immutablearray class, , if have var variable of type immutablearray, can construct whole new immutable array , change variable point new array, particular array object cannot "changed" seen shared reference.