I wonder why ruby give and, or less precedence than &&, || , and assign operator? Is there any reason?
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Marc-André Lafortune
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sarunw
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5 Answers
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My guess is that's a direct carry-over from Perl. The operators or and and were added later in Perl 5 for specific situations were lower precedence was desired.
For example, in Perl, here we wish that || had lower precedence, so that we could write:
try to perform big long hairy complicated action || die ;
and be sure that the || was not going to gobble up part of the action. Perl 5 introduced or, a new version of || that has low precedence, for exactly this purpose.
An example in Ruby where you could use or but not ||:
value = possibly_false or raise "foo"
If you used ||, it would be a syntax error.
the Tin Man
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JRL
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Is there a name for the idiom of do_something or die? Does it get used in ruby? – Andrew Grimm Sep 17 '09 at 00:59
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I don't know of any name for it, but it's fairly common in Ruby. – Chuck Sep 17 '09 at 03:08
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Perl leans heavily on die, whereas Ruby uses raise. The advantage of an exception is you can rescue it. – tadman Sep 17 '09 at 15:20
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Although technically you can rescue from a die, people don't usually bother unless it's really important. It's too much of a nuisance. – tadman Jul 12 '10 at 14:07
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The difference is precedence. ||, && have higher precedence than =, but and, or have lower. So while you can do:
a = nil || 0
You would have to do:
a = (nil or 0)
to get same effect. If you do:
a = nil or 0
The result of expression would still be 0, but a value would be nil.
the Tin Man
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Andrius
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5
They have very low precedence so that the operands don't have to be wrapped in parentheses, as is sometimes the case with && and ||.
the Tin Man
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Chuck
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Being able to control the precedence of your operators is sometimes useful, especially if you are concerned with readability -- extra parenthesis in conditional statements can sometimes obscure the actual logic.
To be frank, though, I think the reason Ruby has the boolean operator precedence levels it does stems mostly from the fact that Matz was a Perl programmer before he ever wrote Ruby, and borrowed much of the core syntax and operators from that language.
rcoder
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hmm, that explains why ruby is so immature and at the same time so much bloated. Still hard to wrap my head around that.. – akostadinov Jun 03 '14 at 16:37
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I believe the idea is specifically to get them below the assignment operators, so you can write logic tests with assignments but without parens.
DigitalRoss
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