Tutorial :Is there any wisdom behind “and”, “or” operators in Ruby?



Question:

I wonder why ruby give and, or less precedence than &&, || , and assign operator? Is there any reason?


Solution:1

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.


Solution:2

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.


Solution:3

They have very low precedence so that the operands don't have to be wrapped in parentheses, as is sometimes the case with && and ||.


Solution:4

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.


Solution:5

I believe the idea is specifically to get them below the assignment operators, so you can write logic tests with assignments but without parens.


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