Sometimes I see variable names with double underscore in the beginning and the end. For example:
Article.__elasticsearch__
Is there some naming convention related to double underscores in Ruby variable names?
An initial underscore or double underscore basically indicates
"special/avoid overwrite" --meaning it's meant to reduce the
likelihood that someone else might define a method/attribute of the
same name. The most common occurrence is __send__.
From Ruby Forum
The author of the ElasticSearch gem made the wrong call IMO. At the end of the thread, Avdi Grimm, who is well-known in the Ruby community, disagrees with the OP.
There's a reason you hadn't seen it yet and that it looks odd to you. It's because it's unidiomatic.
Related
Rails uses it here in rails/activesupport/lib/active_support/inflector/inflections.rb
#__instance__ = Concurrent::Map.new
The meaning is mentioned nowhere in Ruby variable name with double underscores.
The underscore is a legal character in an identifier. It has no meaning whatsoever.
(There is one exception: local variables that start with an underscore will not generate a warning if they are unused.)
In other words: the meaning of #__instance__ is exactly the same as the meaning of #foobar: there is no meaning.
When I was practice in rubular.com, I've be trying to match with a regular expression that checks if a word starts with a non-consonant. My approach it's check cases how that begins with a non-letter, or starts with a number or underscore, or checks the empty string
I've founded a strange behaviour:
My regex /^[aeiou_0-9\W]|^$/i match the k and s consonants!. I don't understand why.
Any ideas?
A link to example -> http://rubular.com/r/0zt0VPmcwr
This is very funny because you have stumbled across a bug specifically for just the letters k and s when using \W with /i (it's like a perfect storm).
Here is the link that explains the bug: https://bugs.ruby-lang.org/issues/4044
Perhaps this was patched in a later version of ruby, but if you don't feel like going through the hassle of going to a new version of ruby, then you can just explicitly make an inverted character class of all the consonants:
/^[^bcdfghjklmnpqrstvwxyz]|^$/i
Here is the rubular link: http://rubular.com/r/URgsWP3suQ
Edit:
So, something else I noticed about your regex is that your regex (and the regex I provided above) matches only the first letter of the words where as the regex that I provided matches the whole word. I don't know if this makes a difference for you, but I felt it was worth pointing out. Please see the difference in the highlighting in the rubular link above and the one below (See how the link above only highlights the first letter of the words where as the link below highlights the whole words):
^[^bcdfghjklmnpqrstvwxyz].*|^$
http://rubular.com/r/IVJ03uOK4h
It is a bug in Ruby regex in some versions. Select version 1.8.7 in the dropdown and you will see your regex works properly.
Edit. Check the docs at http://ruby-doc.org/core-2.1.5/Regexp.html. More specifically, in the metacharacters section:
/\W/ - A non-word character ([^a-zA-Z0-9_]). Please take a look at Bug #4044 if using /\W/ with the /i modifier.
Can someone explain to me what is the difference, in Korn shell, between:
ANOTHER_VAR=${SOME_VAR}
and
ANOTHER_VAR=$SOME_VAR
I came across these types of declaration and can't see what the difference is.
One has two brace characters around the name and the other doesn't; otherwise, in this context, there is no difference.
However, if you had:
ONE_VAR="$TWO_VAR_$THREE_VAR"
UNO_VAR="${TWO_VAR}_${THREE_VAR}"
then the values in $ONE_VAR and $UNO_VAR will be different unless both $TWO_VAR and $TWO_VAR_ exist and $TWO_VAR_ holds the value that is stored in $TWO_VAR plus a trailing underscore (where $TWO_VAR could be an empty string, or undefined, as long as $TWO_VAR_ holds just an underscore).
Thanks to William Pursell for pointing out a minor inaccuracy in the previous version.
There are many contexts where you must use the braces, such as:
UNE_VAR=${YET_ANOTHER_VAR:-"default setting"}
I'm solving http://www.rubeque.com/problems/a-man-comma--a-plan-comma--a-canal--panama-excl-/solutions but I'm a bit confused about treating #{} as comment in regexp.
My code look like this now
def longest_palindrome(txt)
txt[/#{txt.reverse}/]
end
I tried txt[/"#{txt.reverse}"/] or txt[#{txt.reverse}] but nothing works as I wish. How should I implicate variable into regexp?
This is not something you can do with a regex.
While you could use variable interpolation in the construction of a regex (see the other answers/comments), that wouldn't help you here. You could only use that to reverse a literal string, not a regex match result. Even if you could, you still wouldn't have solved the "find the longest palindrome" part, at least not with acceptable runtime performance.
Use a different approach to the problem.
It is hard to tell how do you wish that happens without examples, but I suppose you are after
txt[/#{Regexp.escape(txt.reverse)}/]
See the Regexp#escape method
can any body tell me how to use regex for negation of string?
I wanna find all line that start with public class and then any thing except first,second and finally any thing else.
for example in the result i expect to see public class base but not public class myfirst:base
can any body help me please??
Use a negative lookahead:
public\s+class\s+(?!first|second).+
If Peter is correct and you're using Visual Studio's Find feature, this should work:
^:b*public:b+class:b+~(first|second):i.*$
:b matches a space or tab
~(...) is how VS does a negative lookahead
:i matches a C/C++ identifier
The rest is standard regex syntax:
^ for beginning of line
$ for end of line
. for any character
* for zero or more
+ for one or more
| for alternation
Both the other two answers come close, but probably fail for different reasons.
public\s+class\s+(?:(?!first|second).)+
Note how there is a (non-capturing) group around the negative lookahead, to ensure it applies to more than just the first position.
And that group is less restrictive - since . excludes newline, it's using that instead of \S, and the $ is not necessary - this will exclude the specified words and match others.
No slashes wrapping the expression since those aren't required in everything and may confuse people that have only encountered string-based regex use.
If this still fails, post the exact content that is wrongly matched or missed, and what language/ide you are using.
Update:
Turns out you're using Visual Studio, which has it's own special regex implementation, for some unfathomable reason. So, you'll be wanting to try this instead:
public:b+class:b+~(first|second)+$
I have no way of testing that - if it doesn't work, try dropping the $, but otherwise you'll have to find a VS user. Or better still, the VS engineer(s) responsible for this stupid non-standard regex.
Here is something that should work for you
/public\sclass\s(?:[^fs\s]+|(?!first|second)\S)+(?=\s|$)/
The second look a head could be changed to a $(end of line) or another anchor that works for your particular use case, like maybe a '{'
Edit: Try changing the last part to:
(?=\s|$)