Possible Duplicate:
What does ||= mean in Ruby?
What does ||= mean in Ruby?
views:
191answers:
3
+2
A:
The idea is the same as with other similar operators (+=, *=, etc):
a ||= b is a = a || b
And this trick is not limited to Ruby only: it goes through many languages with C roots.
edit to repel downvoters.
See one of Jörg's links for more accurate approximation, for example this one.
This is exactly why I don't like Ruby: nothing's ever what it seems.
Nikita Rybak
2010-09-27 03:36:39
Notably, not C or C++ or Java.
TokenMacGuy
2010-09-27 03:43:10
@TokenMacGuy I mean general 'trick': producing 'a @= b' from 'a = a @ b'.
Nikita Rybak
2010-09-27 03:49:47
This is wrong. Please read http://Ruby-Forum.Com/topic/151660 and the links provided therein.
Jörg W Mittag
2010-09-27 12:46:49
+6
A:
It's mainly used as a shortform for initializing a variable to a certain value, if it is not yet set.
Think about the statement as returning x || (x = y). If x has a value (other than false), only the left side of the || will be evalutated (since || short-circuts), and x will be not be reassigned. However, if x is false or nil, the right side will be evaluated, which will set x to y, and y will be returned (the result of an assignment statement is the right-hand side).
See http://dablog.rubypal.com/2008/3/25/a-short-circuit-edge-case for more discussion.
Daniel Vandersluis
2010-09-27 03:42:50
`x ||= y` acts like `x = y unless x` which (if we assume x and y stand for arbitrary expressions and not necessarily variables) is *not* the same as either `x = x || y` (consider cases where `x = x` is not a no-op) or `x = y if x.nil?` (consider the case where x is false).
sepp2k
2010-09-27 08:11:04
Jorg W Mittag reckons this is incorrect, in [his answer](http://stackoverflow.com/questions/995593/what-does-mean-in-ruby) to the duplicated question.
Andrew Grimm
2010-09-27 10:38:12
This is wrong. Please read http://Ruby-Forum.Com/topic/151660 and the links provided therein.
Jörg W Mittag
2010-09-27 12:46:32