Feature #12752
closed
Unpacking a value from a binary requires additional '.first'
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)
# ...
Updated by shyouhei (Shyouhei Urabe) over 9 years ago
- Description updated (diff)
Updated by mame (Yusuke Endoh) over 9 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 [email protected]
Updated by naruse (Yui NARUSE) about 9 years ago
How about Array#unpack1 ?
Updated by matz (Yukihiro Matsumoto) about 9 years ago
unpack1 looks so ad-hoc but surely is attractive.
Matz.
Updated by matz (Yukihiro Matsumoto) about 9 years ago
Go ahead.
Matz.
Updated by knu (Akinori MUSHA) about 9 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) about 9 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.
Updated by naruse (Yui NARUSE) about 9 years ago
- Status changed from Open to Closed
Applied in changeset r56959.
String#unpack1 [Feature #12752]
Returns the first value of String#unpack.
