Ruby |= assignment operator

Question

How the |= assignment operator works?

score 77 · Answer 1 · answered Jun 10 '14 at 15:48

77

When working with arrays |= is useful for uniquely appending to an array.

>> x = [1,2,3]
>> y = [3,4,5]

>> x |= y
>> x
=> [1, 2, 3, 4, 5]

answered Jun 10 '14 at 15:48

mlm

score 53 · Accepted Answer · answered Dec 19 '11 at 23:42

53

Bitwise OR assignment.

x |= y

is shorthand for:

x = x | y

(just like x += y is shorthand for x = x + y).

answered Dec 19 '11 at 23:42

mynameiscoffey

Bah, my bad, thanks for the correction. Updated my answer to reflect bitwise or, not logical or. – mynameiscoffey Dec 19 '11 at 23:47

score 14 · Answer 3 · edited Apr 11 '21 at 14:40

14

With the exception of ||= and &&= which have special semantics, all compound assignment operators are translated according to this simple rule:

a ω= b

is the same as

a = a ω b

Thus,

a |= b

is the same as

a = a | b

edited Apr 11 '21 at 14:40

Jeremy Moritz

answered Dec 20 '11 at 01:23

Jörg W Mittag

1

In what ways does `x ||= y` differ from `x = x || y` ? – mynameiscoffey Dec 20 '11 at 15:57
As far as i can tell, `||=` and `&&=` are not exceptions. They both seem to function identically to `a = a || b` and `a = a && b`, respectively. If there are any exceptions to this, can you please provide an example? – Jeremy Moritz Apr 11 '21 at 14:41
2

@JeremyMoritz: If `a` is a setter (e.g. `foo.bar=`), then `a = a || b` will *always* call both the setter and the getter, whereas `a ||= b` will *only* call the setter if `a` is falsey (or truthy in the case of `&&=`). In other words: I can write a program which can output whether you used `||=` or `= … || …`, therefore the two are not equivalent. – Jörg W Mittag Apr 11 '21 at 15:22
2

@JeremyMoritz: Note that this is a bug in the ISO Ruby Language Specification. The ISO spec says that all operator assignments `a ω= b` for all operators `ω` are evaluated AS-IF they were written as `a = a ω b`, but that is only true for operators *other than* `||` and `&&`. – Jörg W Mittag Apr 11 '21 at 15:25
Thank you @JörgWMittag for the detailed explanation! – Jeremy Moritz Apr 12 '21 at 00:16

score 3 · Answer 4 · answered Dec 19 '11 at 23:41

3

It is listed in the link you provided. It's an assignment combined with bitwise OR. Those are equivalent:

a = a | b
a |= b

answered Dec 19 '11 at 23:41

ScarletAmaranth

4 Answers4