Question:

Consider the following code:

var array1 = [1, 2, 3, 4, 5]
var array2 = array1
array2.append(6)
var len = array1.count

What’s the value of the len variable, and why?

Answer:

The len variable is equal to 5, meaning that array1 has 5 elements, whereas array2 has 6 elements:

array1 = [1, 2, 3, 4, 5]
array2 = [1, 2, 3, 4, 5, 6]

When array1 is assigned to array2, a copy of array1 is actually created and assigned.

The reason is that swift arrays are value types (implemented as structs) and not reference types (i.e. classes). When a value type is assigned to a variable, passed as argument to a function or method, or otherwise moved around, a copy of it is actually created and assigned or passed. Note that swift dictionaries are also value types, implemented as structs.

Value types in swift are:

  • structs (incl. arrays and dictionaries)
  • enumerations
  • basic data types (boolean, integer, float, etc.)

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