RCR? Added syntax for chains that possibly return nil

Ruby
1

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

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

2

Excerpts from Stefan R.'s message of Thu Jul 19 16:31:01 +0300
2007:

While all of this is fine, maybe that could be improved. My RCR would be
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

how about this ugly creature?

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

Not exactly like your syntax but gets the job done.

Also, you might want to consider the proper way™ of doing it (I
think)

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.

3

Eugen Minciu wrote:

Excerpts from Stefan R.'s message of Thu Jul 19 16:31:01 +0300
2007:

While all of this is fine, maybe that could be improved. My RCR would be
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

how about this ugly creature?

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 :slight_smile: 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.

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 :-/

Regards
Stefan

4

Eugen Minciu wrote:

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.

Regards
Stefan

5

On 7/19/07, Stefan R. [email protected] wrote:

While all of this is fine, maybe that could be improved. My RCR would be
solution would put the coder in power as to where he cares about getting
Posted via http://www.ruby-forum.com/.

Hmm I thought we have had this already, but I do not think somebody
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

6

On Thu, 19 Jul 2007 22:31:01 +0900, Stefan R. 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?

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.

7

gabriele renzi wrote:

On Thu, 19 Jul 2007 22:31:01 +0900, Stefan R. 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.

Regards
Stefan

8

On 7/19/07, Stefan R. [email protected] wrote:

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 :frowning:

Robert

9

Robert D. wrote:
On 7/19/07, Stefan R. [email protected] 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 :frowning:

Robert

Keyword is “simulate” :wink:
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).

Regards
Stefan

10

On Jul 19, 6:31 am, Stefan R. [email protected] 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.

11

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.)

Regards
Stefan

12

On Jul 19, 3:33 pm, Stefan R. [email protected] 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.

13

Trans wrote:

On Jul 19, 3:33 pm, Stefan R. [email protected] 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.

Regards
Stefan

14

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)

-Stephen

15

On 7/19/07, Stefan R. [email protected] wrote:

stuff or just spread it onto a bit more of lines.
Unlike e.g. making nil to respond to every method returning self, this

Posted via http://www.ruby-forum.com/.

More things should yield on success (and not yield on failure) instead
of
(or in addition to) returning nil.

def process_line
gets do |line|
line.chomp.bar { |o| o.baz }
end
end

while process_line
end

of course this particular example is much better written as

ARGF.each_line do |line|
line.chomp …
end

anyway

16

Excerpts from Stefan R.'s message of Fri Jul 20 01:06:13 +0300
2007:

Robert

Keyword is “simulate” :wink:
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).

Regards
Stefan

Hi, again
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() :slight_smile:

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:innilsafe’
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 … :wink:

Let me know what you think of this one
Cheers,

–
Eugen Minciu.

Wasting valuable time since 1985.

17

On Jul 19, 4:35 pm, “Stephen D.” [email protected] 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.

18

On Jul 19, 4:34 pm, Stefan R. [email protected] wrote:

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.

19

Hi,

At Fri, 20 Jul 2007 08:35:20 +0900,
Stephen D. 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

20

Nobuyoshi N. wrote:

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… :-/

Regards
Stefan