Feature #14609
openLet `Kernel#p` without an argument print the receiver
Description
Abstract¶
Kernel#p(obj)
prints obj
as inspect
ed.
How about printing the receiver if an argument is not given?
Background¶
We recently introduced yield_self
, which encourages block chain.
https://zverok.github.io/blog/2018-01-24-yield_self.html
Quoting from this article, we can write method chain with blocks:
construct_url
.yield_self { |url| Faraday.get(url) }.body
.yield_self { |response| JSON.parse(response) }
.dig('object', 'id')
.yield_self { |id| id || '<undefined>' }
.yield_self { |id| "server:#{id}" }
There is a small problem concerning debugging.
If we want to see the intermediate values in the method/block chain, we need to insert tap{|e| p e}
.
With the above example,
construct_url
.yield_self { |url| Faraday.get(url) }.body
.yield_self { |response| JSON.parse(response) }.tap{|e| p e} # debug print
.dig('object', 'id')
.yield_self { |id| id || '<undefined>' }.tap{|e| p e} # debug print
.yield_self { |id| "server:#{id}" }
Proposal¶
Let obj.p
work the same as p(obj)
.
We can replace
block{...}.tap{|e| p e}
with
block{...}.p
For the above example, we can simply add .p
at the end of a line:
construct_url
.yield_self { |url| Faraday.get(url) }.body
.yield_self { |response| JSON.parse(response) }.p # debug print
.dig('object', 'id')
.yield_self { |id| id || '<undefined>' }.p # debug print
.yield_self { |id| "server:#{id}" }
Compatibility issues¶
(1) Shorthand for nil
This spec change can introduce compatibility issues because p
returns nil
and does not output anything.
That is to say, p
is a shorthand for nil
. Some code-golfers use it.
Maybe we can ignore them :p
(2) make it a public method
Kernel#p
a is private method, so if we mistype obj.x
as obj.p
(not sure how it is feasible), it will raise a NoMethodError
because of visibility.
We need to change this behavior.
Note¶
Past proposal and discussion¶
Endoh-san proposed the same idea 10+ years ago [ruby-dev:29736] in Japanese.
I think we should revisit this idea because of yield_self
introduction.
In this thread, Matz said "simple p
shows p(self)
, it is not clear".
p
はどう動くのかとか(p selfと同じ、は変な気が)
self.p(obj)
はどうなのかとか。その辺が解決(納得)できたら、ということで。
English translation:
What would the behavior of:
p
be? (I feel strange for it to be equivalent to `p(self)`.) What would happen to
self.p(obj)
pp¶
If this proposal is accepted, we also need to change the behavior of pp
.
gems¶
tapp
method is provided by a gem.
https://github.com/esminc/tapp
I thought about proposing this method in core. But I found that p
is shorter than tapp
.
A disadvantage is that p
is too short and difficult to grep.
Updated by mame (Yusuke Endoh) over 6 years ago
+1
Kernel#p
is one of the greatest feature in Ruby. It would be further great to make it useful.
Updated by zverok (Victor Shepelev) over 6 years ago
Small notice: If #13581 would be once acted upon, attaching p
in the middle of the chain could be as simple as (using one of the proposed syntaxes)
.yield_self { |response| JSON.parse(response) }.tap(&:.p)
.dig('object', 'id')
.yield_self { |id| id || '<undefined>' }.tap(&:.p)
Just .p
is still nicer, though.
Updated by Hanmac (Hans Mackowiak) over 6 years ago
hm i have a slightly problem with this
check out the different return types there:
a = []
p *a #=> nil
a = [1]
p *a #=> 1
a = [1,2]
p *a #=> [1,2]
Updated by ko1 (Koichi Sasada) about 6 years ago
Hanmac: do you rely on this behavior?
Updated by Hanmac (Hans Mackowiak) about 6 years ago
ko1 (Koichi Sasada) wrote:
Hanmac: do you rely on this behavior?
Me? not so much, in general i don't trust the return value of print commands (print returns null)
it was months ago, i probably wanted to point out that the return value of p
might be differ depending on the parameters
It might be inconsistency?
There is Object.display
too but i don't use it much because it doesn't have new lines
Updated by osyo (manga osyo) about 6 years ago
Good proposal.
This can solve the following problem.
# NG: syntax error, unexpected ':', expecting '}'
p { name: "homu", age: 14 }
# OK:
{ name: "homu", age: 14 }.p
# => {:name=>"homu", :age=>14}
Updated by nobu (Nobuyoshi Nakada) about 6 years ago
osyo (manga osyo) wrote:
Good proposal.
This can solve the following problem.# NG: syntax error, unexpected ':', expecting '}' p { name: "homu", age: 14 }
You can use parentheses.
p(name: "home", age: 14)
Updated by shevegen (Robert A. Heiler) about 6 years ago
I don't mind, personally. To me, the biggest improvement was
that we could omit doing:
require 'pp'
;)
Since I did that a lot in my code. (I love pp; I think I use it
more than just p)
I personally have not been using (or needing) yield_self or tap so
far, so the change would probably not be of immediate benefit to
me; but probably also not require of me to change anything either.
To the name "tapp" - that name is a bit weird. To me it reads as
if we combine "tap" and then add a "p" to it. Reminds me of a
joke proposal to condense "end" into "enddd" and such. :D
To be fair, I consider the name yield_self to be also weird :D -
but matz added an alias called "then" to it if I understand it
correctly (though the semantic confuses me a bit as well ... but
I don't really want to distract here since I don't really feel
too strongly either way; picking good names is not always easy).
On a side note, perhaps in the long run we could have something
to "experiment" with - like new or changed features in ruby that
have not been 100% approved in the sense of a name AND the associated
functionality, so we can try them out for some time, which may help
build a stronger opinion either way. (I mean this in general, not
just in regards to #p here).
It may still be best to ask matz again though. Syntax shortcuts
(syntactic sugar) has always been an area in ruby where code changes
has happened (e. g. yield_self to then, or omitting the end value
for infinite ranges and so forth).
Updated by nobu (Nobuyoshi Nakada) about 6 years ago
How about:
self.P
:P
Updated by matz (Yukihiro Matsumoto) about 6 years ago
I vote for #tapp.
Matz.
Updated by mrkn (Kenta Murata) about 6 years ago
- Related to Feature #15112: Introducing the short form of `STDERR.puts expr.inspect`. added
Updated by docx (Lukas Dolezal) about 6 years ago
Allowing debugging within yield_self
is great! If yield_self
was inspired by Elixir, we can look at Elixir for inspiration here as well:
https://hexdocs.pm/elixir/IO.html#inspect/2
One of the examples that is very interesting is that they have optional parameter to describe the printout:
[1, 2, 3]
|> IO.inspect(label: "before")
|> Enum.map(&(&1 * 2))
|> IO.inspect(label: "after")
|> Enum.sum
Prints:
before: [1, 2, 3]
after: [2, 4, 6]
I'm wondering, would that be something we would like in Ruby too?
The problem with the proposal of making obj.p
is that the same method already is defined with parameter in the form of p(obj)
.
Hence it would be impossible to implement obj.p("after")
- as that would conflict with the current version of p
with parameter.
My feeling is that given that both yield_self
and tap
are defined on Object
, it does not feel to me right that .p
should be defined on Kernel
. I can see the advantage of already existing method there, but I feel like it would be wrong overloading.
Continuing on the argument that yield_self
is defined on Object
, should we define this "print inspect and return self" method be defined on Object too
?
If so, we could make new method p_self
(terrible name yes) and implement it with new interface when called as instance method and avoid making Kernel.p
public:
Object.p_self() - p self and return self
Object.p_self(label:) - puts "#{label}: #{self.inspect}" and return self
What do you think?
Updated by zverok (Victor Shepelev) about 6 years ago
@docx (Lukas Dolezal) That are pretty interesting comparison with Elixir!
In fact, what the examples show (to me) is a need for more powerful partial application of procs. E.g. what would be a parity for Elixir is something like...
def p_with_label(label, obj)
puts "#{label}#{obj.inspect}"
end
[1, 2, 3]
.tap(&method(:p_with_label).curry['before: '])
.map { |x| x * 2 }
.tap(&method(:p_with_label).curry['after: '])
.sum
This example already works, yet doesn't look VERY expressive, to be honest. I see two pretty different solutions to the problem:
First is core. Considering the shorten of &method(:name)
is discussed for ages (and almost agreed to be &:.name
), it could be discussed on addition of more powerful partial application than current (mostly unusable) Proc#curry
to language core. The result may look somewhat like (fantasizing)...
[1, 2, 3]
.tap(&:.p.with('before: '))
.map { |x| x * 2 }
.tap(&:.p.with('after: '))
.sum
The second one is rise of proc-producing libraries:
module Functional
module_function
def inspect(label:)
->(obj) { puts "#{label}#{obj.inspect}" }
end
end
[1, 2, 3]
.tap(&Functional.inspect(label: 'before: '))
.map { |x| x * 2 }
.tap(&Functional.inspect(label: 'after: '))
.sum
Updated by nobu (Nobuyoshi Nakada) about 6 years ago
zverok (Victor Shepelev) wrote:
First is core. Considering the shorten of
&method(:name)
is discussed for ages (and almost agreed to be&:.name
),
You may want to say &self.:name
at https://bugs.ruby-lang.org/issues/13581#change-72072?
It wouldn't be able to omit the receiver, syntactically.
Updated by zverok (Victor Shepelev) about 6 years ago
It wouldn't be able to omit the receiver, syntactically.
Hmm, I missed this point is the discussion. This limitation makes :.
syntax sugar substantially less useful :(
Updated by ko1 (Koichi Sasada) about 6 years ago
How about obj.p!
or obj.pp!
?
Updated by akr (Akira Tanaka) over 5 years ago
matz (Yukihiro Matsumoto) wrote:
I vote for #tapp.
I don't like #tappp (for pp self
).
Updated by ko1 (Koichi Sasada) over 5 years ago
Discussion:
-
obj.p
has compatibility issue (some code expectp
returnsnil
) -> reject -
p!
is not danger. -> reject -
tapp
seems long.tappp
is weird -
tap_p
,tap_pp
are too long. - introduce
obj.?
new method name -> don't modify syntax! (by matz). it is not predicate.
No conclusion.
Updated by larskanis (Lars Kanis) over 4 years ago
+1 for obj.p
, but I don't like the alternative names. IMHO obj.p
is the natural extension of Kernel#p
. Any other name doesn't feel right. Does the current p() => nil
really justify a reject of such a useful feature?
Updated by jeremyevans0 (Jeremy Evans) over 4 years ago
larskanis (Lars Kanis) wrote in #note-21:
+1 for
obj.p
, but I don't like the alternative names. IMHOobj.p
is the natural extension ofKernel#p
. Any other name doesn't feel right. Does the currentp() => nil
really justify a reject of such a useful feature?
I don't code like this is a major issue:
def foo
p
end
That seems unlikely to occur in real world code as it doesn't do anything useful. Where I think you get into compatibility issues is code like:
def foo
debug = []
debug << 1 if something
debug << 2 if something_else
p(*debug)
end
Here, you would expect no output, not outputting of the receiver.
Updated by sawa (Tsuyoshi Sawada) over 4 years ago
- Subject changed from `Kernel#p` without args shows the receiver to Let `Kernel#p` without an argument print the receiver
- Description updated (diff)
Updated by sawa (Tsuyoshi Sawada) over 4 years ago
What about obj.tap
?
construct_url
.then{|url| Faraday.get(url)}
.body
.then{|response| JSON.parse(response)}.tap
.dig('object', 'id')
.then{|id| id || '<undefined>'}.tap
.then{|id| "server:#{id}"}
Currently, tap
without a block raises a LocalJumpError
, so it would not have compatibility issues. Furthermore, the meaning of the word "tap" matches such behavior.
Updated by mame (Yusuke Endoh) over 2 years ago
- Related to Feature #18736: self-p for method chain added
Updated by hsbt (Hiroshi SHIBATA) 7 months ago
- Status changed from Open to Assigned