pass-by-object definition

pass-by-object.markdown

pass-by-object

• variables reference objects

    a = 1
    b = a

  b references 1, not a

  Corollary: it is not possible to change the reference of a variable indirectly

    a = 1
    b = a
    a = 2

  b still references 1

• the value which is passed is the object, not the variable

    a = 1
    foo(a)

  In this example, the value 1 is passed, not the variable a.

• a mutation of the object (if it is mutable) will be visible everywhere the object is referenced

    a = [1,2,3]
    b = a
    foo(a) # foo appens the value 4 to the array
    a # => [1,2,3,4] - a still references the same object, but the object has been mutated
    b # => [1,2,3,4] - since b references the same object as a, the mutation is visible there too

• it's not possible to change which object a variable references from out-of-scope (e.g. after a = obj; foo(a), a will always still reference the same object as before the call)