RCR? Added syntax for chains that possibly return nil
Stefan Rusterholz
readability is working around cases where an intermediate method might
return nil. Those cases are e.g.
while (line = gets && line.chomp)
foo = (bar && bar.baz && bar.baz.quuz) || default # bar might be nil, so
might bar.baz and bar.baz.quuz
There are some more constructs, most of you surely already used such
stuff or just spread it onto a bit more of lines.
While all of this is fine, maybe that could be improved. My RCR would be
to introduce a new syntax besides . for method invocation, which on the
first nil aborts any further method calls on it and returns nil.
E.g. the above examples would become:
while line = gets->chomp
foo = bar->baz->quuz || default
-> was the first best that came to my mind, if you have better ideas,
please state.
Unlike e.g. making nil to respond to every method returning self, this
solution would put the coder in power as to where he cares about getting
nil (e.g. he wants an exception if foo is nil, so he just writes
foo.bar, if he doesn't want one, he writes foo->bar) and where he just
wants to get the nil value back.
Do you think this RCR is worth to make?
Regards
Stefan
--
Posted via http://www.ruby-forum.com/.
Eugen Minciu
<hack>
class Object
alias regular_method_missing method_missing
def method_missing(meth)
if meth.to_s[0]=='_'[0]
return nil
else
regular_method_missing(meth)
end
end
end
puts "yay, it works" unless 3._foo._bar._baz
</hack>
Not exactly like your syntax but gets the job done.
Also, you might want to consider the proper way(tm) of doing it (I think)
<proper way>
begin
foo.bar.baz.whatever
rescue
puts "yay it works"
end
</proper way>
Also works as a one liner:
x = begin 3.foo.bar.baz; rescue; nil; end
--
Eugen Minciu.
Wasting valuable time since 1985.
Stefan Rusterholz
> Excerpts from Stefan Rusterholz's message of Thu Jul 19 16:31:01 +0300
> 2007:
>> nil (e.g. he wants an exception if foo is nil, so he just writes
>> foo.bar, if he doesn't want one, he writes foo->bar) and where he just
>> wants to get the nil value back.
>>
>> Do you think this RCR is worth to make?
>>
>> Regards
>> Stefan
>>
> how about this ugly creature?
>
> <hack>
> class Object
> alias regular_method_missing method_missing
> def method_missing(meth)
> if meth.to_s[0]=='_'[0]
> return nil
> else
> regular_method_missing(meth)
> end
> end
> end
Interesting idea :) This one won't work right away I think, but it's a
starting point.
Btw., you can do ?_ instead of '_'[0]. Syntax would have the benefit of
optimization, though.
> <proper way>
> begin
> foo.bar.baz.whatever
> rescue
> puts "yay it works"
> end
You'd have to rescue NoMethodError, since else you could miss important
exceptions. For the same reason, single line rescue is disqualified. And
with a rescue, it is even less readable than working around the nil case
via multiple lines :-/
Robert Dober
made such a concise proposal yet; I am slightly in favor, but gotta
think a lot about it before giving a definite vote, just wanted to
give you some positive feed back for now...
Robert
--
I always knew that one day Smalltalk would replace Java.
I just didn't know it would be called Ruby
-- Kent Beck
Stefan Rusterholz
> <hack>
> class Object
> alias regular_method_missing method_missing
> def method_missing(meth)
> if meth.to_s[0]=='_'[0]
> return nil
> else
> regular_method_missing(meth)
> end
> end
> end
Reworked it a bit:
class Object
alias method_missing_no_underscore method_missing
def method_missing(m,*a,&b)
m.to_s[0] == ?_ ? send(m.to_s[1..-1],*a,&b) :
method_missing_no_underscore(m,*a,&b)
end
end
class NilClass
alias method_missing_no_underscore method_missing
def method_missing(m,*a,&b)
m.to_s[0] == ?_ ? nil : method_missing_no_underscore(m,*a,&b)
end
end
while line = gets._chomp
..
end
so ._ simulates -> with that hack. Thanks for the idea. Should check for
m.to_s != "_", though, since that method is used e.g. with gettext.
gabriele renzi
> Do you think this RCR is worth to make?
Sorry, I may have missed this in the previous thread, but why an inline
rescue clause is not enough?
i.e.
while (line = gets && line.chomp)
foo = (bar && bar.baz && bar.baz.quuz) || default # bar might be nil, so
might bar.baz and bar.baz.quuz
could be
while line = gets.chomp rescue nil
foo = bar.baz.quuz rescue default
end
I admit I have a strange feeling about a raising loop condition.. but
something like the second line I wrote many times.
This is slightly longer and gives you a little bit less control,
but I think that complex one-line flow control may be a bad thing.
Just my two cents, obviously.
--
goto 10: http://www.goto10.it
blog it: http://riffraff.blogsome.com
blog en: http://www.riffraff.info
Stefan Rusterholz
> On Thu, 19 Jul 2007 22:31:01 +0900, Stefan Rusterholz wrote:
>
>
>> Do you think this RCR is worth to make?
>
> Sorry, I may have missed this in the previous thread, but why an inline
> rescue clause is not enough?
> while line = gets.chomp rescue nil
> foo = bar.baz.quuz rescue default
> end
Simple: what if your exception is not the NoMethodError you are worried
about? You'll never know.
Or less dramatic: a bug may stay in your app unnoticed for longer than
necessary.
Robert Dober
> end
>
> so ._ simulates -> with that hack. Thanks for the idea. Should check for
> m.to_s != "_", though, since that method is used e.g. with gettext.
>
> Regards
> Stefan
>
> --
> Posted via http://www.ruby-forum.com/.
>
I hate it, this really should be syntax and furthermore it would make
code ugly ( I know beauty lies in the eyes of the beholder ;).
The original idea is quite good, why your shift?
This is a terrible name pollution amongst other bad things :(
Stefan Rusterholz
On 7/19/07, Stefan Rusterholz <ape...@gmx.net> wrote:
>> so ._ simulates -> with that hack.
> I hate it, this really should be syntax and furthermore it would make
> code ugly ( I know beauty lies in the eyes of the beholder ;).
> The original idea is quite good, why your shift?
>
> This is a terrible name pollution amongst other bad things :(
>
> Robert
Keyword is "simulate" ;-)
This can help trying it out. And I fully agree, that hack is ugly, also
I wouldn't use it in actual code simply because it is "magic" (you have
to know that _* methods are magic, that's not good for code to be
maintained).
Trans
On Jul 19, 6:31 am, Stefan Rusterholz <apei...@gmx.net> wrote:
> One type of construct in ruby that somewhat annoys me and IMHO reduces
> readability is working around cases where an intermediate method might
> return nil. Those cases are e.g.
>
> while (line = gets && line.chomp)
> foo = (bar && bar.baz && bar.baz.quuz) || default # bar might be nil, so
> might bar.baz and bar.baz.quuz
what about
foo = bar.baz.quuz rescue default
T.
Stefan Rusterholz
> what about
> foo = bar.baz.quuz rescue default
See the answer to gabriele renzi (Simple: what if your exception is not
the NoMethodError you are worried
about? You'll never know.)
Trans
On Jul 19, 3:33 pm, Stefan Rusterholz <apei...@gmx.net> wrote:
> Trans wrote:
> > what about
> > foo = bar.baz.quuz rescue default
>
> See the answer to gabriele renzi (Simple: what if your exception is not
> the NoMethodError you are worried
> about? You'll never know.)
I think it rescues all StandardErrors.
T.
Stefan Rusterholz
Um, Yes, that's exactly the problem about it, wasn't that clear? It
rescues *all* StandardErrors. So you won't notice if something else than
your NoMethodError - which nil would raise - has happened.
Say your gets raises a BrokenPipe exception or similar since the server
you were connected disconnects you because of bad input you send. Your
will never see an exception being raised since that happens in the gets
you just rescue all standarderrors from.
Eugen Minciu
I've been thinking about this a bit more. Here's another approach you
could try. This actually feels a lot less like a hack.
Advantages:
- no namespace pollution
- clarifies what you're trying to do
Disadvantage:
- every time you call it you add an extra, intermediary call to, well,
call() :)
However, I'm sure that I'm getting something wrong and, again, you can
simplify this to some extent, and improve it. It's just the idea itself
that I wanted to show you. I'm certain you'll find a way to ditch the
call()
def nilsafe(&blk)
x=Proc.new { Object.method_missing }
def method_missing(meth,*args,&blk)
return nil
end
begin
yield blk
rescue => e
def method_missing(meth,*args,&blk)
x.call(meth,args,&blk)
end
raise e
end
def method_missing(meth,*args,&blk)
x.call(meth,args,&blk)
end
end
So from an IRB prompt, after loading it, you can do:
irb(main):002:0> 3.foo.bar.bz
NoMethodError: undefined method `foo' for 3:Fixnum
from (irb):2
irb(main):003:0> nilsafe { 3.foo.bar.baz }
=> nil
irb(main):004:0> nilsafe do
irb(main):005:1* 3.foo.bar.baz
irb(main):006:1> raise "Some Error here"
irb(main):007:1> end
RuntimeError: Some Error here
from (irb):6
from ./safeattr2.rb:8:in `nilsafe'
from (irb):4
from :0
the raise could be changed a little to output some nicer results (using caller) and other such niceties. But it is late now ... ;)
Let me know what you think of this one
Cheers,
Trans
On Jul 19, 4:35 pm, "Stephen Duncan" <stephen.dun...@gmail.com> wrote:
> Not sure if the existence of features in other languages is generally
> considered a good support for RCR's, but Groovy has this feature:http://groovy.codehaus.org/Statements#Statements-Safenavigation(though the
> syntax can't be borrowed)
One could ask for something close:
bar.?.boo.?.quuz
But that's still pretty ick, though it could do that now with a
regular method.
T.
Trans
On Jul 19, 4:34 pm, Stefan Rusterholz <apei...@gmx.net> wrote:
> Trans wrote:
> > On Jul 19, 3:33 pm, Stefan Rusterholz <apei...@gmx.net> wrote:
> >> Trans wrote:
> >> > what about
> >> > foo = bar.baz.quuz rescue default
>
> >> See the answer to gabriele renzi (Simple: what if your exception is not
> >> the NoMethodError you are worried
> >> about? You'll never know.)
>
> > I think it rescues all StandardErrors.
>
> > T.
>
> Um, Yes, that's exactly the problem about it, wasn't that clear? It
> rescues *all* StandardErrors. So you won't notice if something else than
> your NoMethodError - which nil would raise - has happened.
> Say your gets raises a BrokenPipe exception or similar since the server
> you were connected disconnects you because of bad input you send. Your
> will never see an exception being raised since that happens in the gets
> you just rescue all standarderrors from.
So a better RCR maybe it just to qualify the line rescue.
NoMethodError being the more common, maybe a special rescue for that.
Eg.
bar.baz.quuz ||| default
T.
Nobuyoshi Nakada
At Fri, 20 Jul 2007 08:35:20 +0900,
Stephen Duncan wrote in [ruby-talk:260854]:
> Not sure if the existence of features in other languages is generally
> considered a good support for RCR's, but Groovy has this feature:
> http://groovy.codehaus.org/Statements#Statements-Safenavigation (though the
> syntax can't be borrowed)
It reminded me of a patch in `[ruby-dev:28217] ANDCALL
operator'. It was &? though.
http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-dev/28217
--
Nobu Nakada
Stefan Rusterholz
> It reminded me of a patch in `[ruby-dev:28217] ANDCALL
> operator'. It was &? though.
>
> http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-dev/28217
Oh, what does it do, or how to use it? I'm sorry, my japanese doesn't go
beyond hajime and tatame... :-/
Robert Dober
look at this example
bar->baz.foo, which has to be written as
(bar.baz ||| default).foo
of course one could write
bar.baz.foo ||| default
but it has more permissive semantics and will hide errors that
bar->baz.foo
will raise
Trans
On Jul 20, 6:29 am, "Robert Dober" <robert.do...@gmail.com> wrote:
> On 7/20/07, Trans <transf...@gmail.com> wrote:
>
> Hmm I like the expressiveness of the original proposal
> look at this example
>
> bar->baz.foo, which has to be written as
> (bar.baz ||| default).foo
>
> of course one could write
> bar.baz.foo ||| default
> but it has more permissive semantics and will hide errors that
> bar->baz.foo
> will raise
> Robert
But where is default in your example? You'd have:
(bar->baz || default).foo
T.
Robert Dober
But -> does not support default, that is a feature of your solution.
I have completely overlooked this :(, the -> notation implies nil as default.
And you are thus right about the example above, your idea is indeed powerful :)
Robert
> T.
Stefan Rusterholz
Maybe you should reread the initial proposal. There is no default.
In receiver->method, if receiver is nil, method won't be invoked and the
expressions value is nil. If the receiver isn't nil, method is invoked
on receiver just as with a normal . - HTH
regards
Stefan Rusterholz
> On 7/20/07, Trans <tran...@gmail.com> wrote:
>> >
>>
> But -> does not support default, that is a feature of your solution.
> I have completely overlooked this :(, the -> notation implies nil as
> default.
>
> And you are thus right about the example above, your idea is indeed
> powerful :)
>
> Robert
Well, default can still be established with ->, just the plain old way:
foo = bar->baz || default # if anywhere in the chain is nil, you get the
default
Trans
On Jul 20, 7:18 am, Stefan Rusterholz <apei...@gmx.net> wrote:
> Robert Dober wrote:
> > On 7/20/07, Trans <transf...@gmail.com> wrote:
>
> > But -> does not support default, that is a feature of your solution.
> > I have completely overlooked this :(, the -> notation implies nil as
> > default.
>
> > And you are thus right about the example above, your idea is indeed
> > powerful :)
>
> > Robert
>
> Well, default can still be established with ->, just the plain old way:
> foo = bar->baz || default # if anywhere in the chain is nil, you get the
> default
Sure. I realize. I'm only pointing out that this -> operator is
equivalent to a rescue NoMethodError, so maybe we just need a way to
specify that better, rather then a whole new dispatcher which can
greatly hurt code readability, IMHO. So a keyword besides 'rescue'
might do the trick, maybe 'default' would be better? I just thru |||
out there b/c of it's similarity to ||. So...
foo = bar.baz default nil
Another possibility... perhaps we can add a feature to #tap (which has
already been added to Ruby 1.9) so that:
foo = bar.tap.baz
does the trick.
T.
Stefan Rusterholz
> Sure. I realize. I'm only pointing out that this -> operator is
> equivalent to a rescue NoMethodError,
So how can I explain to you that it *isn't*?
> Another possibility... perhaps we can add a feature to #tap (which has
> already been added to Ruby 1.9) so that:
Somebody else here on the list uses a method 'ergo' to do what -> would
do. Similar disadvantages as the ._methods solution.
Trans
On Jul 20, 9:36 am, Stefan Rusterholz <apei...@gmx.net> wrote:
> Trans wrote:
> > Sure. I realize. I'm only pointing out that this -> operator is
> > equivalent to a rescue NoMethodError,
>
> So how can I explain to you that it *isn't*?
Just tell me, how isn't it? The end result seems exactly the same me.
How does:
foo = (bar.baz default bar).quuz default quux
differ in result from:
foo = (bar->baz || bar)->quuz || quux
> > Another possibility... perhaps we can add a feature to #tap (which has
> > already been added to Ruby 1.9) so that:
>
> Somebody else here on the list uses a method 'ergo' to do what -> would
> do. Similar disadvantages as the ._methods solution.
Ah, right. I like #ergo, but it's not quite that same as this -> as it
only applied to nil. Wouldn't -> be more like:
def arrow
@_op ||= Functor.new{ |op, *args|
begin
self.send(op, *args)
rescue NoMethodError
nil
end
}
end
T.
ara.t.howard
On Jul 19, 2007, at 7:31 AM, Stefan Rusterholz wrote:
> One type of construct in ruby that somewhat annoys me and IMHO reduces
> readability is working around cases where an intermediate method might
> return nil. Those cases are e.g.
i feel your pain, however i feel that moves towards calling things
and having the side effect ignored will lead to new classes of subtle
bugs. for instance
path.gsub! File::SEPARATOR, '\\'
returns nil for no sub for a reason: i may be an error if no
substitution was done...
still, i agree there are cases where i makes sense to chain/ignore
>
> while (line = gets && line.chomp)
while( (line = gets or break).chomp )
end
but i'm just playing devil's advocate there ;-)
> foo = (bar && bar.baz && bar.baz.quuz) || default # bar might be
> nil, so
> might bar.baz and bar.baz.quuz
>
> There are some more constructs, most of you surely already used such
> stuff or just spread it onto a bit more of lines.
> While all of this is fine, maybe that could be improved. My RCR
> would be
> to introduce a new syntax besides . for method invocation, which on
> the
> first nil aborts any further method calls on it and returns nil.
>
> E.g. the above examples would become:
> while line = gets->chomp
> foo = bar->baz->quuz || default
>
> -> was the first best that came to my mind, if you have better ideas,
> please state.
> Unlike e.g. making nil to respond to every method returning self, this
> solution would put the coder in power as to where he cares about
> getting
> nil (e.g. he wants an exception if foo is nil, so he just writes
> foo.bar, if he doesn't want one, he writes foo->bar) and where he just
> wants to get the nil value back.
>
> Do you think this RCR is worth to make?
it does, but in the meantime we can use something like:
http://drawohara.tumblr.com/post/6304449
a @ http://drawohara.com/
--
we can deny everything, except that we have the possibility of being
better. simply reflect on that.
h.h. the 14th dalai lama
Nobuyoshi Nakada
At Fri, 20 Jul 2007 19:02:59 +0900,
Stefan Rusterholz wrote in [ruby-talk:260938]:
> > It reminded me of a patch in `[ruby-dev:28217] ANDCALL
> > operator'. It was &? though.
> >
> > http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-dev/28217
>
> Oh, what does it do, or how to use it? I'm sorry, my japanese doesn't go
> beyond hajime and tatame... :-/
In short, same as your proposal.
(tmp = h[:a] and tmp[:b])
can be without the temproray variable:
h[:a]&?[:b]
and
h.a and h.a.b
can be:
h.a&?b
And a followup was to make nil? to take a block which is
called when the receiver isn't nil.
--
Nobu Nakada
Stefan Rusterholz
> In short, same as your proposal.
> (tmp = h[:a] and tmp[:b])
> can be without the temproray variable:
> h[:a]&?[:b]
>
> and
> h.a and h.a.b
> can be:
> h.a&?b
>
> And a followup was to make nil? to take a block which is
> called when the receiver isn't nil.
Ah, interesting, so I'm not the first to propose this :)
What was the reason it was rejected?
Trans
On Jul 20, 10:18 am, Trans <transf...@gmail.com> wrote:
> On Jul 20, 9:36 am, Stefan Rusterholz <apei...@gmx.net> wrote:
>
> > Trans wrote:
> > > Sure. I realize. I'm only pointing out that this -> operator is
> > > equivalent to a rescue NoMethodError,
>
> > So how can I explain to you that it *isn't*?
>
> Just tell me, how isn't it? The end result seems exactly the same me.
> How does:
>
> foo = (bar.baz default bar).quuz default quux
>
> differ in result from:
>
> foo = (bar->baz || bar)->quuz || quux
I went back and reread the first post. You actually want it to only be
effective on nil. Okay, I see the basic difference. In my example if
bar.baz returned nil then the default quux would be the result. In
yours it would be bar. However, I'm not sure that's better. I can just
do
foo = (bar.baz || bar).quuz default quux
to get your behavior. But your technique can not do what mine can.
T.
no...@ruby-lang.org
At Sat, 21 Jul 2007 03:21:53 +0900,
Stefan Rusterholz wrote in [ruby-talk:261012]:
> Ah, interesting, so I'm not the first to propose this :)
> What was the reason it was rejected?
It wasn't rejected, at least explicitly. Just no response.
--
Nobu Nakada
Robert Dober
I do not like either of the syntaxes but these are two bright ideas
nevertheless, I feel that the power of Tom's solution somehow
justifies the syntax.
Ara's point is important too, how big are chances that this syntax
will be abused of?
But it is not as important as it might seem at first sight <ducking>
as we have already shown that there are equivalent language constructs
anyway...
.. still thinking.
>
>
Robert
Thomas Gantner
> ...
>
> foo = bar.baz default nil
>
> Another possibility...
>
I prefer this solution to the otherwise also very elegant variant with '->'.
With 'default' (or '|||' or ...) we can also catch all the syntactically
special methods like '==' '<=>', '[]', all the operators ('&', '*', ...)
etc.
-Thomas
--
Thomas Gantner mailto:thomas....@gmx.net
<sig. under construction>
Daniel DeLorme
> Trans wrote:
>> Sure. I realize. I'm only pointing out that this -> operator is
>> equivalent to a rescue NoMethodError,
>
> So how can I explain to you that it *isn't*?
rescue NoMethodError has the same disadvantage as rescue StandardError;
it may catch errors that you did not intend to. e.g.:
foo = Object.new
def foo.bar
baz()
end
foo.bar->boo
=> NoMethodError: undefined method `baz'
begin
foo.bar.boo
rescue NoMethodError
end
=> nil
>> Another possibility... perhaps we can add a feature to #tap (which has
>> already been added to Ruby 1.9) so that:
>
> Somebody else here on the list uses a method 'ergo' to do what -> would
That would be me
> do. Similar disadvantages as the ._methods solution.
except with less namespace pollution :-P
I have to admit the -> keyword would be better. With ergo I have to
propagate the check to every step of the call chain:
a.b.ergo.c.ergo.d.ergo.e
where -> would allow a simple
a.b->c.d.e
(assuming that you only want to guard against b being nil)
But since other languages (e.g. PHP) use -> for method access, I think
we would see a lot of newbies blindly using -> for all method calls and
then wondering why things go awry. Maybe ".?" would be better? Or maybe
we're over-thinking and this feature isn't really used often enough to
warrant its own operator and a more verbose form like ergo is enough...
Daniel
Robert Dober
> Stefan Rusterholz wrote:
> > Trans wrote:
> >> Sure. I realize. I'm only pointing out that this -> operator is
> >> equivalent to a rescue NoMethodError,
> >
> > So how can I explain to you that it *isn't*?
>
> rescue NoMethodError has the same disadvantage as rescue StandardError;
> it may catch errors that you did not intend to. e.g.:
This is a little detail I have overseen in the discussion
-> *is not* equivalent to rescue NoMethodError, if I have understood correctly
a-> b
is
begin
a.b
rescue NoMethodError
raise unless a.nil?
===========
end
Robert