Closures in Ruby about dylanninin.com

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# ---------------------------- Section 5: Rant ----------------------------
#
# This is quite a dizzing array of syntactic options, with subtle semantics differences that are not
# at all obvious, and riddled with minor special cases. It's like a big bear trap from programmers who
# expect the language to just work.
#
# Why are things this way? Because Ruby is:
#
#   (1) designed by implementation, and
#   (2) defined by implementation.
#
# The language grows because the Ruby team tacks on cool ideas, without maintaining a real spec apart
# from CRuby. A spec would make clear the logical structure of the language, and thus help highlight
# inconsistencies like the ones we've just seen. Instead, these inconsinstencies creep into the language,
# confuse the crap out of poor souls like me who are trying to learn it, and then get submitted as bug
# reports. Something as fundamental as the semantics of proc should not get so screwed up that they have
# to backtrack between releases, for heaven's sake! Yes, I know, language design is hard -- but something
# like this proc/lambda issue or the arity problem wasn't so hard to get right the first time.
# Yammer yammer.

# ---------------------------- Section 6: Summary ----------------------------
#
# So, what's the final verdict on those 7 closure-like entities?          
#
#                                                     "return" returns from closure
#                                    True closure?    or declaring context...?         Arity check?
#                                    ---------------  -----------------------------    -------------------
# 1. block (called with yield)       N                declaring                        no
# 2. block (&b => f(&b) => yield)    N                declaring                        no
# 3. block (&b => b.call)            Y except return  declaring                        warn on too few
# 4. Proc.new                        Y except return  declaring                        warn on too few
# 5. proc                                    <<< alias for lambda in 1.8, Proc.new in 1.9 >>>
# 6. lambda                          Y                closure                          yes, except arity 1
# 7. method                          Y                closure                          yes
#
# The things within each of these groups are all semantically identical -- that is, they're different
# syntaxes for the same thing:
#   
#      1. block (called with yield)
#      2. block (&b  =>  f(&b)  =>  yield)  
#      -------
#      3. block (&b  =>  b.call)
#      4. Proc.new  
#      5. proc in 1.9
#      -------
#      5. proc in 1.8
#      6. lambda    
#      -------
#      7. method (may be identical to lambda with changes to arity checking in 1.9)
#
# Or at least, this is how I *think* it is, based on experiment. There's no authoritative answer other
# than testing the CRuby implementation, because there's no real spec -- so there may be other differences
# I haven't discovered.

Reference

additional references

• https://innig.net/software/ruby/closures-in-ruby