Feature #13395
openAdd a method to check for not nil
Description
There does not seem to be a method in Ruby to check if an object is not nil.
Such a method could help with readability.
Example:
array = [1, 'dog', nil] array.count(&:not_nil?)
vs
array = [1, 'dog', nil] array.reject(&:nil?).count
Updated by sawa (Tsuyoshi Sawada) over 7 years ago
Many methods that take a block come in positive-negative pairs, unlike count
. I am not sure how frequent the use case is, but if it is, I rather claim that there should be a negative version of count
.
Updated by duerst (Martin Dürst) over 7 years ago
Any ideas about the name?
Updated by Hanmac (Hans Mackowiak) over 7 years ago
array.count(&:itself)
does work for something similar like that.
its not 100% what you might want, because it does ignore false
too
Updated by nobu (Nobuyoshi Nakada) over 7 years ago
Hanmac (Hans Mackowiak) wrote:
array.count(&:itself)
does work for something similar like that.
IIRC, it equals to simple array.count
.
Updated by Hanmac (Hans Mackowiak) over 7 years ago
nobu (Nobuyoshi Nakada) wrote:
Hanmac (Hans Mackowiak) wrote:
array.count(&:itself)
does work for something similar like that.
IIRC, it equals to simple
array.count
.
are you sure? i am currently on ruby 2.3.3 Windows
[1, "bc", nil].count #=> 3
[1, "bc", nil].count(&:itself) #=> 2
Updated by nobu (Nobuyoshi Nakada) over 7 years ago
Thank you for the correction.
Updated by ogarci5 (Oliver Garcia) over 7 years ago
What about as a condition for if statements? For example:
Case 1
if !object.nil?
# Do something
end
Case 2
if object
# Do something
end
Case 3
if object.not_nil?
# Do something
end
I end up using Case 2 a lot because it reads better than Case 1. However this doesn't work if object can be false in which case Case 3 would be the most readable.
Updated by darix (Marcus Rückert) over 7 years ago
if !object.nil? # Do something end
unless object.nil?
# Do something
end
Updated by shevegen (Robert A. Heiler) over 7 years ago
I think that these discussions come up with some frequency; if I recall correctly,
Tsuyoshi Sawada was proposing something that I agreed with in principle. But I
did point out that the english language appears to have it easier with positive
assertions rather than negative ones.
I am not against .not_nil?
per se, mind you, since it may be symmetrical for .nil?
cases and the example give by darix (if nil
, if !nil?
, unless nil?
) but I think
it is something that is somewhat showing a limitation of the english language as
such.
I actually found that the simplest way, for my own code, is to try to formulate
things "positively" whenever possible.
So:
if condition
end
if condition1 and condition2
end
A similar explanation I use for .select
or .reject
, I
almost always go to pick exactly what I need to have.
Like a filter where you apply the filtering in a
forward fashion (you could of course always revert the
filter, like to use .reject
rather than .select
, or
within the block clause, invert the checks).
To the suggestion itself in regards to .count
, perhaps
this may be worthwhile to have some special meaning for
what a user may want to count for.
In non-legal ruby, consider this:
array = [1, 'dog', nil]
array.count(! &:nil?)
Granted, not very readable. :)
Then again, I also consider the & not really readable either.
How about:
array = [1, 'dog', nil]
array.count(:not_nil)
or
array.count(:not_nil)
Hmm...
To be honest, I don't think that these examples are really that
great.
In the above example, using .compact
may be simpler:
array.compact.size
For the latter, perhaps a method that does it, like .not_nil? but
I am not sure if this is used that much to warrant an addition.
I do somewhat agree with ogarci5 by the way - not necessarily because
of the explanation, but because in case 3 he gave, you do not have
to use "unless
" and neither the invert "operator" "!
", which is
usually much easier and more straightforward. So in that context,
I actually agree, having that flexibility may be a good thing,
even if I don't like the name .not_nil?
a lot.
I still think that it is a limitation of the english language.
Consider a backpack in a RPG/rogue-like game. You want to
query whether it is empty or filled:
if backpack.empty? # Seems simple.
if !backpack.empty? # Seems ok although more difficult to understand
if backpack.filled? # Hmmm... filled with what?
if backpack.not_empty? # Not ideal but perhaps also better than the other two examples before
So I kinda semi-agree with ogarci5; I still think that the english language
itself is the one that has the biggest problems here with negations, followed
by the human brain modeling concepts. (OOP is a modeled concept too after all)
Updated by kernigh (George Koehler) over 7 years ago
Because !
is a method, one can also write !object.nil?
as object.nil?.!
using the method chain .nil?.!
to check for not nil. This works since Ruby 1.9, if I recall.
Updated by nobu (Nobuyoshi Nakada) over 7 years ago
- Related to Feature #12075: some container#nonempty? added
Updated by matz (Yukihiro Matsumoto) about 7 years ago
Your example is bit weak. Is there any realistic use-case for the method?
Matz.
Updated by znz (Kazuhiro NISHIYAMA) about 7 years ago
I think Array#nitems
is like this. But it was removed since ruby 1.9.1.
In doc/NEWS-1.9.1:
o Array#nitems was removed (use count {|i| !i.nil?})
Updated by MSP-Greg (Greg L) about 7 years ago
I believe the english equivalent to not_nil
would be exist
(instead of exists, to follow prev use). I believe core only uses exist?
with Dir
, File
, and FileTest
.
Having it would allow showing the standard case first in an if-else-end structure, given that unless-else-end may be considered 'strange' code.
Also, I'm sure many of us have used a tri-state nil/false/true variable when it is helpful.