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Feature #12752

Unpacking a value from a binary requires additional '.first'

Added by tagomoris (Satoshi TAGOMORI) over 2 years ago. Updated over 2 years ago.

Status:
Closed
Priority:
Normal
Assignee:
-
Target version:
-
[ruby-core:77249]

Description

When I parsed a binary protocol (msgpack) by String#unpack, there are many similar expressions, like below:

str = io.read(1)
length = str.unpack('C').first
case length
when 4
  data = io.read(4).unpack('N').first
# ...

I know that unpack returns "1 or more" values, but I think there are too many cases to return just one object.
Creating Array objects for return values requires additional cost to create Array object, and calling .first.

I'm happy if I can write the code above like this:

str = io.read(1)
length = str.unpack('C', 0) # index, or str.unpack('C', index: 0)
case length
when 4
  data = io.read(4).unpack('N', 0)
# ...

Associated revisions

Revision 306f43ac
Added by naruse (Yui NARUSE) over 2 years ago

String#unpack1 [Feature #12752]

Returns the first value of String#unpack.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56959 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

Revision 56959
Added by naruse (Yui NARUSE) over 2 years ago

String#unpack1 [Feature #12752]

Returns the first value of String#unpack.

Revision 56959
Added by naruse (Yui NARUSE) over 2 years ago

String#unpack1 [Feature #12752]

Returns the first value of String#unpack.

Revision 56959
Added by naruse (Yui NARUSE) over 2 years ago

String#unpack1 [Feature #12752]

Returns the first value of String#unpack.

Revision 56959
Added by naruse (Yui NARUSE) over 2 years ago

String#unpack1 [Feature #12752]

Returns the first value of String#unpack.

History

Updated by shyouhei (Shyouhei Urabe) over 2 years ago

  • Description updated (diff)

Updated by mame (Yusuke Endoh) over 2 years ago

There is more concise way:

length, = str.unpack('C')

You cannot use this in a method chain, though.

I actually understand your frustration, but I feel no difference between str.unpack('C', 0) and str.unpack('C')[0].

--
Yusuke Endoh mame@ruby-lang.org

Updated by naruse (Yui NARUSE) over 2 years ago

How about Array#unpack1 ?

Updated by matz (Yukihiro Matsumoto) over 2 years ago

unpack1 looks so ad-hoc but surely is attractive.

Matz.

Updated by knu (Akinori MUSHA) over 2 years ago

With a qualifier or multiple directives given, would it raise an ArgumentError or just go ahead with the process and only return the first value?

Updated by naruse (Yui NARUSE) over 2 years ago

Akinori MUSHA wrote:

With a qualifier or multiple directives given, would it raise an ArgumentError or just go ahead with the process and only return the first value?

Just after processing the first value, it returns.

#8

Updated by naruse (Yui NARUSE) over 2 years ago

  • Status changed from Open to Closed

Applied in changeset r56959.


String#unpack1 [Feature #12752]

Returns the first value of String#unpack.

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