Bug #16496
closed
Numbered Parameter not parsed properly in lambda
Description
The space between * and 1 changes the lambda behaviour, looks like numbered parameter _1 is not parsed properly
2.7.0 :001 > l = -> { _1 * 1 }
2.7.0 :002 > l[2]
=> 2
2.7.0 :003 > l2 = -> { _1 *1 }
2.7.0 :004 > l2[2]
Traceback (most recent call last):
5: from /Users/justin.feng/.rvm/rubies/ruby-2.7.0/bin/irb:23:in `<main>'
4: from /Users/justin.feng/.rvm/rubies/ruby-2.7.0/bin/irb:23:in `load'
3: from /Users/justin.feng/.rvm/rubies/ruby-2.7.0/lib/ruby/gems/2.7.0/gems/irb-1.2.1/exe/irb:11:in `<top (required)>'
2: from (irb):4
1: from (irb):3:in `block in irb_binding'
ArgumentError (wrong number of arguments (given 1, expected 0))
2.7.0 :005 >
Updated by mame (Yusuke Endoh) over 5 years ago
- Status changed from Open to Rejected
_1 *1 is parsed as _1(*1), a call to a method _1 with a variable-length argument with 1. It is the same as p * ary and p *ary. You can see a warning under verbose mode:
$ ruby -w -e '-> { _1 *1 }.call'
-e:1: warning: `*' interpreted as argument prefix
...
It is difficult to change until a method name _1 is valid.
Updated by JustinFeng (Justin Feng) over 5 years ago
mame (Yusuke Endoh) wrote:
_1 *1is parsed as_1(*1), a call to a method_1with a variable-length argument with1. It is the same asp * aryandp *ary. You can see a warning under verbose mode:$ ruby -w -e '-> { _1 *1 }.call' -e:1: warning: `*' interpreted as argument prefix ...It is difficult to change until a method name
_1is valid.
Hi Yusuke, thank you for the reply, good to understand what caused the issue
However, it just makes me feel the numbered parameter behaves different from traditional block parameter
2.7.0 :001 > l = lambda {|p| p *1 }
2.7.0 :002 > l[2]
=> 2
2.7.0 :003 > l = lambda {|p| p * 1 }
2.7.0 :004 > l[2]
=> 2
Updated by JustinFeng (Justin Feng) over 5 years ago
- Status changed from Rejected to Feedback
Updated by mame (Yusuke Endoh) over 5 years ago
We are now migrating. If we change it immediately, a program that uses _1 as a method name will break. So it is now warned:
warning: `_1' is reserved for numbered parameter; consider another name
After enough time, we will be able to prohibit _1 as a method name, and _1 can be always used as a numbered parameter. So please wait for a few years.
Updated by jeremyevans0 (Jeremy Evans) over 5 years ago
- Status changed from Feedback to Rejected