CODEWITHSUNDEEP
swift
Boon
Boon

Reputation: 41480

Is there a way to determine if a variable passed in is reference type or value type?

In Swift, is there a way to determine through code if a variable passed in is reference type or value type?

For example, is tuple a value type or reference type?

Upvotes: 5

Views: 623

Answers (2)

matt
matt

Reputation: 535232

Everything is a value type except for:

  • An instance of a class

  • A function

  • An array (which works in an odd way; it is passed by reference but can become unbound from its other avatars if it is mutable and the number of items is changed)

The simple code way to test is just to assign to two different var names, change one, and see if they are still equal. For example:

    var tuple1 = (1,2)
    var tuple2 = tuple1
    tuple1.1 = 3
    println(tuple1)
    println(tuple2)

They are different, proving that a tuple is passed by value. But:

    var arr1 = [1,2]
    var arr2 = arr1
    arr1[1] = 3
    println(arr1)
    println(arr2)

They are the same, proving that an array is passed by reference.

EDIT:

But in beta 3 of Swift, this unusual behavior of Array is withdrawn, and only class instances and functions are passed by reference. Everything else is passed by value now.

Upvotes: 6

YarGnawh
YarGnawh

Reputation: 4654

afaik, to pass by reference you need to add the inout keyword in front of the parameter definition. all other parameters are constants unless prefixed with the var keyword

“Function parameters are constants by default. Trying to change the value of a function parameter from within the body of that function results in a compile-time error. This means that you can’t change the value of a parameter by mistake.”

and...

“Variable parameters, as described above, can only be changed within the function itself. If you want a function to modify a parameter’s value, and you want those changes to persist after the function call has ended, define that parameter as an in-out parameter instead.”

Excerpt From: Apple Inc. “The Swift Programming Language.” iBooks. https://itun.es/us/jEUH0.l

Upvotes: 1

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