Bug #18837
closedNot possible to evaluate expression with numbered parameters in it
Description
I presume it's not really a bug, but design flaw, but this is really frustrating. Use case is - debugger.
Here is script with expected behavior:
def dumper(bnd)
puts bnd.local_variable_get 'i'
puts bnd.eval 'i * 10'
end
[1,2].each { |i| dumper(binding) }
And this one attempts to do the same with numbered params:
def dumper(bnd)
puts bnd.local_variable_get('_1')
puts bnd.eval '_1 * 10'
end
[1,2].each do
some = _1 # without this line even local_variable_get won't work, still it may be in any place of block
dumper(binding)
end
But eval
wont ever work and this necessity for using _1
so binding could see it may be confusing as well.
Updated by mame (Yusuke Endoh) over 2 years ago
- Related to Feature #15915: `@1` cannot be achieved in meta-programming added
Updated by mame (Yusuke Endoh) over 2 years ago
I talked a bit with some of the committers.
@ko1 (Koichi Sasada) said that it is difficult to retrieve _1
afterwards due to the current implementation limitation, since the actual arguments may be dropped by optimization when a block that does not accept formal arguments is called.
Also, @znz (Kazuhiro NISHIYAMA) pointed out that the meta-programming API to read out only _1
is somewhat unreasonable, since the meaning of _1
depends on the presence of _2.
{ 1 => "A" }.each do
p _1 #=> [1, "A"]
end
{ 1 => "A" }.each do
p _1 #=> 1
_2
end
Updated by mame (Yusuke Endoh) over 2 years ago
- Status changed from Open to Rejected
We discussed this issue at the dev meeting. @matz (Yukihiro Matsumoto) agreed that it is difficult to support this for the reasons I said in #note-2.
Updated by alanwu (Alan Wu) almost 2 years ago
- Related to Feature #19137: Numbered parameters are not made available to IRB. added
Updated by nobu (Nobuyoshi Nakada) 8 months ago
- Has duplicate Bug #20308: `it` and numbered parameters do not work in `eval` added