Hi all,
I’m looking for a bit of help. I can’t seem to get the block to “pass
through” to the parent class. I figured without an ‘&’ in the parameter
list there would be no conversion to proc but maybe that is not the
case.
class Nstring < String
def gsub!(*args)
super
end
end
This works as I expected:
s = Nstring.new(“hi”)
s.gsub!(/(hi)/,’\1’)
=> “hi”
But this, not so much:
s.gsub!(/(hi)/) {$1}
=> “”
Thanks,
Lou
On Thu, Jul 31, 2008 at 11:06 AM, Lou Z. [email protected] wrote:
end
s.gsub!(/(hi)/) {$1}
=> “”
Hi,
This worked for me:
irb(main):023:0> class NString < String
irb(main):024:1> def gsub!(*args, &blk)
irb(main):025:2> super(*args, &blk)
irb(main):026:2> end
irb(main):027:1> end
=> nil
irb(main):028:0> s = NString.new(“hi”)
=> “hi”
irb(main):029:0> s.gsub!(/(hi)/){$1}
=> “hi”
Hope this helps,
Jesus.
Hi,
This worked for me:
irb(main):023:0> class NString < String
irb(main):024:1> def gsub!(*args, &blk)
irb(main):025:2> super(*args, &blk)
irb(main):026:2> end
irb(main):027:1> end
=> nil
irb(main):028:0> s = NString.new(“hi”)
=> “hi”
irb(main):029:0> s.gsub!(/(hi)/){$1}
=> “hi”Hope this helps,
Jesus.
Hi Jesus, thank you for your response. Unfortunately, I could not
replicate your results:
class NString < String
def gsub!(*args, &blk)
super(*args, &blk)
end
end
=> nils = NString.new(“hi”)
=> “hi”s.gsub!(/(hi)/){$1}
=> “”
Perhaps it is my version of ruby?
~$ ruby -v
ruby 1.8.6 (2008-03-03 patchlevel 114) [universal-darwin9.0]
Lou
Mikael, I can deal with that, I’ll swap out the $'s with block params.
Thanks for the workaround!
Lou
On Jul 31, 2008, at 19:10, Lou Z. wrote:
=> “”
Looks like this is a problem with using $1 inside the block. Replacing
{$1} with {|m| m} makes it work.
However, a different issue I now remember running into a long time ago
is that super is pretty quirky regarding blocks:
Calling it as just super will pass the block.
super(*args, &block) will as well, obviously.
super(*args) will too!
The only way to avoid passing the block to super is super(*args, &nil), however ugly that might be.
All of this is tested in 1.8.6, and is probably the same in 1.9.
ERRATUM
use
replace str[0…-1] or
replace str.dup
instead of
replace str
bad mistake of my part sorry.
Robert
On Thu, Jul 31, 2008 at 7:10 PM, Lou Z. [email protected] wrote:
irb(main):028:0> s = NString.new(“hi”)
replicate your results:class NString < String
def gsub!(*args, &blk)
super(*args, &blk)
end
end
=> nil
your problem has nothing to do with passing the block along in gsub!
s = NString.new(“hi”)
guess what s is here?
If you guessed “”, you guessed correctly
=> “hi”
s.gsub!(/(hi)/){$1}
=> “”
normal given that s was “”
Probably subclassing is not what you want, but it can be accomplished of
course
Here is the final solution
class NString < String
def initialize str
replace str
end
def gsub! *args
super( *args, &Proc::new ) # that is just to show you yet another
way to do this but passing &blk is better
end
end
n = Nstring::new( “123”)
p n
p n.gsub!(/…/){ |m| m.reverse } # $1 is not set as somebody did
point out already
HTH
Robert
–
http://ruby-smalltalk.blogspot.com/
There’s no one thing that’s true. It’s all true.
your problem has nothing to do with passing the block along in gsub!
s = NString.new(“hi”)
guess what s is here?
If you guessed “”, you guessed correctly
Wait, why would s be empty? I can use Nstring.new just like String.new
class Nstring < String
end
=> niln = Nstring.new(“hi”)
=> “hi”puts n
hi
Lou
If you guessed “”, you guessed correctly
Wait, why would s be empty? I can use Nstring.new just like String.new
class Nstring < String
end
=> niln = Nstring.new(“hi”)
=> “hi”puts n
you are right I am wrong, no idea what I did OMG.
Seems your only problem was the $1 in the block
Sorry for the noise
R.
On Thu, Jul 31, 2008 at 1:47 PM, Lou Z. [email protected] wrote:
n = Nstring.new(“hi”)
=> “hi”
puts n
hi
Same here:
seltzer:~ sandal$ ruby -v
ruby 1.8.6 (2008-06-20 patchlevel 230) [i686-darwin8.11.1]
seltzer:~ sandal$ irb
class NString < String
end
=> nil
n = NString.new(“hi”)
=> “hi”
puts n
hi
That having been said, I generally avoid sub-classing core Ruby
objects because I think some of them use optimizations that cause
internal C methods to be called rather than the methods of a subclass,
resulting in strange behaviour. That having been said, I don’t know
that I’ve ever seen it in practice. Does anyone have an example of
this, or am I just being paranoid?
-greg
Lou Z. wrote:
Mikael, I can deal with that, I’ll swap out the $'s with block params.
Thanks for the workaround!Lou
Actually, this did not work the way I expected. It is fine for a case
like this:
str = “match1”
gsub!(/(match1)/) {|m| m}
But not this:
str = “match1match2”
gsub!(/(match1)(match2)/) {|m1,m2| m1 + m2}
Where I am really looking for:
str = “match1match2”
gsub!(/(match1)(match2)/) { $1 + $2}
So let me ask this instead: How do I pass a block from one method to
another without invoking the block?
For instance, let’s say I want to create a method nsub! that behaves
EXACTLY like gsub!
class String
def nsub!(*args)
gsub!(args[0]) {yield}
end
end
This will not work, say I do this:
s = String.new(“whatever”)
s.nsub!(/(what)/) {$1}
The yield in the body of nsub! invokes the block {$1}, but in this
context $1 is nil, so it is like I am calling
gsub!(args[0]) {nil}
Which is obviously not what I want. I would like to pass the original
code block:
gsub!(args[0]) {$1}
Any ideas?
Lou
On Thu, Jul 31, 2008 at 4:51 PM, Lou Z. [email protected] wrote:
Which is obviously not what I want. I would like to pass the original
code block:gsub!(args[0]) {$1}
Any ideas?
If you don’t mind a little redundancy, you can match the string first,
pull the MatchData object, and yield that:
class String
def nsub!(*args)
m = match(args[0])
gsub!(args[0]) { yield(m) }
end
end
=> nil
str = “match1match2”
=> “match1match2”
str.nsub!(/(match1)(match2)/) { |m| m[1] + “—” + m[2] }
=> “match1—match2”
str
=> “match1—match2”
It would be nice if MatchData was yielded by gsub instead of a string.
-greg
On Thu, Jul 31, 2008 at 11:03 PM, Gregory B.
[email protected] wrote:
It would be nice if MatchData was yielded by gsub instead of a string.
-greg
Well, maybe, but do not despair, while the $ special variables are not
available in the block Regexp.last_match is
506/6 > cat gsub.rb && ruby gsub.rb
‘abc’.gsub(/(.)(.)/){ p Regexp.last_match }
#<MatchData “ab” 1:“a” 2:“b”>
http://ruby-smalltalk.blogspot.com/
There’s no one thing that’s true. It’s all true.
But unfortunately, this does not fix your problem:
Indeed. But all is not lost. I think this will work fine for what I
need to do (it’s tweaked from the solution you gave earlier, thank you).
class String
def nsub!(*args)
if m = match(args[0])
gsub!(args[0]) {yield(*m.to_a[1…-1])}
end
end
end
s = “match1match2”
=> “match1match2”s.nsub!(/(match1)(match2)/) {|m1,m2| m2 + m1}
=> “match2match1”
I haven’t done much with it yet, but from some preliminary tests it
seems to work.
Thanks for the help everyone!
Lou
On Thu, Jul 31, 2008 at 7:10 PM, Lou Z. [email protected] wrote:
irb(main):028:0> s = NString.new(“hi”)
replicate your results:
Sorry, it seems that my $1 was set by previous tests in IRB
The others are right and the discussion has been interesting.
It also shows you have to be careful with tests in IRB…
Jesus.
On Thu, Jul 31, 2008 at 4:51 PM, Lou Z. [email protected] wrote:
another without invoking the block?
I forgot to answer this before:
class String
def nsub!(*args,&block)
gsub!(args[0],&block)
end
end
But unfortunately, this does not fix your problem:
str = “match1match2”
=> “match1match2”
str.nsub!(/(match1)(match2)/) { |m| $1 + “—” + $2 }
NoMethodError: undefined method `+’ for nil:NilClass
On Fri, Aug 1, 2008 at 7:54 AM, Jesús Gabriel y
Galán[email protected] wrote:
Sorry, it seems that my $1 was set by previous tests in IRB
The others are right and the discussion has been interesting.
It also shows you have to be careful with tests in IRB…
I know that and I still managed to screw up my String subclass
constructor :-(. But I agree, interesting thread, always
good to refresh some “basic” things.
Cheers
Robert
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