Forum: Ruby ! and ? in function name

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Tony (Guest)
on 2006-03-21 19:03
Hi Ruby-rulez !

I often look at some code, for example un rails/active_record, where
functions name end with a ? or a !

Is this a special notation, meaning that the func or args or whatever
have some treatment before/after the body ? Or to show that the function
return a boolean (?) and the arg modified (!) ?

Thanx ;)
Justin C. (Guest)
on 2006-03-21 19:10
Tony wrote:
> Hi Ruby-rulez !
>
> I often look at some code, for example un rails/active_record, where
> functions name end with a ? or a !
>
> Is this a special notation, meaning that the func or args or whatever
> have some treatment before/after the body ? Or to show that the function
> return a boolean (?) and the arg modified (!) ?
>
> Thanx ;)

Generally the (?) means it returns a boolean and (!) means it modifies
the receiver (the object the method is being called on) in place, rather
than creating a new object.

For example:

irb(main):001:0> a = "Hello"
=> "Hello"
irb(main):002:0> a.include?('e')
=> true
irb(main):003:0> a.reverse
=> "olleH"
irb(main):004:0> a
=> "Hello"                     #unmodified
irb(main):005:0> a.reverse!
=> "olleH"                     #modified
irb(main):006:0> a
=> "olleH"


Hope that helps.

-Justin
Jacob F. (Guest)
on 2006-03-21 19:11
(Received via mailing list)
On 3/21/06, Tony <removed_email_address@domain.invalid> wrote:
> Hi Ruby-rulez !
>
> I often look at some code, for example un rails/active_record, where
> functions name end with a ? or a !
>
> Is this a special notation, meaning that the func or args or whatever
> have some treatment before/after the body ? Or to show that the function
> return a boolean (?) and the arg modified (!) ?

The latter. The ? and ! characters in a method name have absolutely no
import to the parser/interpreter (well, no more import than does any
other character such as 'f' or 'q'). They only serve, by convention,
as an indicator to the programmer of the behavior of the method.

Jacob F.
13 (Guest)
on 2006-03-21 19:12
(Received via mailing list)
Hi,

Here is an excerpt from the free online version of the Programming
Ruby book [1]:

...
Methods that act as queries are often named with a trailing ``?'',
such as instance_of?. Methods that are ``dangerous,'' or modify the
receiver, might be named with a trailing ``!''. For instance, String
provides both a chop and a chop!. The first one returns a modified
string; the second modifies the receiver in place. ``?'' and ``!'' are
the only weird characters allowed as method name suffixes.
..

[1] http://www.rubycentral.com/book/tut_methods.html

Martins
Tony (Guest)
on 2006-03-21 19:18
Thanks to all !

And specially Martin, because I read the given page twice today but
never the first paragraph, answering my (stupid) question.
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