Return_on

Ruby
1

Sometimes i do this:

return x if x

Anyway to code it as:

return_on x

t.

2

Trans schrieb:

Sometimes i do this:

return x if x

Anyway to code it as:

return_on x

It’s not very nice, but you could wrap the whole method body in a block
and use throw/catch behind the scenes.

Regards,
Pit

3

On 1/10/07, Trans [email protected] wrote:

Sometimes i do this:

return x if x

Anyway to code it as:

return_on x

I cannot recall I ever have used return, in this way,
but my coding style may be 5% different than yours.
Maybe I can improve my minimal insight.

Any good (larger) examples of this thing?

4

Trans wrote:

Sometimes i do this:
return x if x
Anyway to code it as:
return_on x

I’m wondering if continuations (or continuations + set_trace_func to
catch the method end) could be used to achieve that, but am not a whiz
at callcc, and am up past my bedtime (hence am not going to experiment
w/ it).

Is there a Weirich in the house?

Devin
(Even if it can be implemented using such hackery, I might consider that
a smell that it’s so different, and doesn’t map to Ruby’s ways, and be
hesitant to use such a beast in GP code.)

5

On 10-Jan-2007, at 20:09, Trans wrote:

Sometimes i do this:

return x if x

Anyway to code it as:

return_on x

t.

I do this quite often, as well! We need a macro system :wink:

JS

6

Simon S. wrote:

I cannot recall I ever have used return, in this way,
but my coding style may be 5% different than yours.
Maybe I can improve my minimal insight.

Any good (larger) examples of this thing?

I don’t really have any examples that are repleat with it, but as to
insight it’s especially convenient when caching a return value:

def x
return_on @cache[:x]
# do stuff
@cache[:x] = result_of_stuff
end

this gets rid of an extraneous variable too b/c otherwise, the more
efficient impl. is:

def x
r = @cache[:x]
return r if r
# do stuff
@cache[:x] = result_of_stuff
end

funny thing i just came across a similar case for break. how would you
DRY this up and get rid of ‘result’?

result = nil
files.each do
  result = require file
  break if result
end
if result
  ...

t.

7

Trans schrieb:

efficient impl. is:

def x
r = @cache[:x]
return r if r
# do stuff
@cache[:x] = result_of_stuff
end

You could also implement this as

def x
@cache[:x] ||= (
# do stuff
result_of_stuff
)
end

funny thing i just came across a similar case for break. how would you
DRY this up and get rid of ‘result’?

result = nil
files.each do
  result = require file
  break if result
end
if result
  ...

If “result” is only a flag whose value you don’t need later, you could
do

if files.find { |file| require file }
…
end

Regards,
Pit

8

Trans wrote:
…

funny thing i just came across a similar case for break. how would you
DRY this up and get rid of ‘result’?

result = nil
files.each do
  result = require file
  break if result
end
if result
  ...

This only helps a little…

result = files.each do |file|
r = require file and break r
end

9

“Trans” [email protected] writes:

def x
return_on @cache[:x]
# do stuff
@cache[:x] = result_of_stuff
end

def x
@cache.fetch(:x) {
@cache[:x] = result_of_stuff
}
end

10

On Wed, Jan 10, 2007 at 11:39:00PM +0900, Trans wrote:

Sometimes i do this:

return x if x

Anyway to code it as:

return_on x

t.

This is pure unadulterated evil, however it did come up in #ruby-lang a
while ago, so I whipped up some good old fashioned homemade evil:

def try_return(&block)
unless (blah = block.call).nil?
GC.disable
eval(“return ObjectSpace._id2ref(#{blah.object_id})”, block)
end
ensure
GC.enable
end

def f
try_return { nil }
try_return { 7 }
0
end

p f

11

Trans wrote:

funny thing i just came across a similar case for break. how would you
DRY this up and get rid of ‘result’?

result = nil
files.each do
  result = require file
  break if result
end
if result
  ...

Well, this is much easier:

if files.any? {|file| require file }
…

C’mon, Trans. :slight_smile:

Devin
(Or am I missing something obvious?)

12

I have made the most hackish thing to accomplish this. It is basically
a regexp-supporting preprocessor. I don’t recommend using it.

#! /usr/bin/ruby -w

def preprocessor_define(*args, &blk)

Determine line of caller

callerLine = caller.join.match(/[0-9]+/)[0].to_i

Get the source of the running file

source = IO.read(FILE)

Remove the callerLine line

source = source.split("\n")
source.delete_at(callerLine - 1)
source = source.join("\n")

Do the replacement

source.gsub!(*args, &blk)

Avoid function redefinition warnings

newName = “”
50.times {newName << (rand(26) + 65).chr }
source.gsub!(“preprocessor_define”, newName)

Run the replacement

#puts source
eval source
exit
end

preprocessor_define(/return_on (.*)/) {|s| “return #{s[1]} unless
#{s[1]}.nil?”}

def test
zulu = 5
return_on zulu
puts “Broken.”
end
test

Output: None, as ‘puts Broken’ never gets executed.

13

On 1/13/07, Trans [email protected] wrote:

def x
return r if r
break if result
end
if result
…

t.

Much like returning in ActiveSupport:
http://weblog.jamisbuck.org/2006/10/27/mining-activesupport-object-returning

  • rob
14

Daniel F. wrote:

source = IO.read(FILE)
newName = “”
#{s[1]}.nil?"}

def test
zulu = 5
return_on zulu
puts “Broken.”
end
test

Output: None, as ‘puts Broken’ never gets executed.

Holy Smokes! The Man goes out of his way!!! return_on brother,
return_on! :slight_smile:

T.

15

On Jan 14, 1:34 am, “Trans” [email protected] wrote:

def x
return_on @cache[:x]
# do stuff
@cache[:x] = result_of_stuff
end

def x
@cache[:x] ||= begin
# do stuff
end
end

Gavin

16

Pit C. wrote:

this gets rid of an extraneous variable too b/c otherwise, the more

def x
@cache[:x] ||= (
# do stuff
result_of_stuff
)
end

That pretty good. I rarely use ( ) as local encapsulator and probably
should consider it more often. I’m generally partial to less indention
when I can get it though.

Thanks,
T.

17

Rob S. wrote:

Much like returning in ActiveSupport:
Buckblog: Mining ActiveSupport: Object#returning

Yes, kind-a. However there’s been a lot of focus on the more common
method cache usecase, but return_on could also be used multple times
too:

def x(a,b)
return_on foo(a)
return_on foo(b)
,
end

T.

18

Joel VanderWerf wrote:

This only helps a little…

result = files.each do |file|
r = require file and break r
end

…and the use of ‘and’. these are the crafty of ruby :slight_smile:

def x
r = @cache[:x] and return r
…
end

pretty good, still a little unDRY, but pretty good.

t.

19

Joel VanderWerf wrote:

@cache[:x] ||= begin
)

CACHING
“oof”
“oof”

It doesn’t work correctly.

def reverse x
@cache[:x] ||= (
puts “CACHING”
x.reverse
)
end

@cache = {}

p reverse(“foo”)
p reverse(“what?”)
p reverse(“And this is cached, you think???”)

— output -----
CACHING
“oof”
“oof”
“oof”

20

Devin M. wrote:

  ...

Well, this is much easier:

if files.any? {|file| require file }
…

Cool, I forget that #any? will break after the first true encounter. I
used #find as pit suggested (which can return any value actually). But,
that wasn’t really my point. Such a solution breaks the analogy to the
original return case --whihc can’t be DRYed-up that way.

T.