Bug #16748: Different behaviour between a hash and multi-Array when passing 2 arguments to a proc

• Status: Rejected
• Assignee: -
• Target version: -
• ruby -v: 2.7.0
• Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN

[Mattruby (Matthew Nash)]

In Ruby 2.5.5 i get what i'm expecting

test = -> (one, two) { one }
[['one', 'two']].map(&test)
=> ["one"]

In Ruby 2.7.0 this doesn't work

test = -> (one, two) { one }
[['one', 'two']].map(&test)
wrong number of arguments (given 1, expected 2) (ArgumentError)

[Mattruby (Matthew Nash)]

• File Screen Shot 2020-04-01 at 16.47.37.png Screen Shot 2020-04-01 at 16.47.37.png added

[mame (Yusuke Endoh)]

• Description updated (diff)

[mame (Yusuke Endoh)]

• Status changed from Open to Rejected

The behavior of 2.5.5 was wrong. Array#map yields each element, in this case, ['one', 'two'], an array of two elements. The lambda requires two arguments, but one array is passed, which should raise "wrong number of arguments".

You may want to use -> (ary) { ary[0] } instead of -> (one, two) { one }. Or you can use proc {|one, two| one }.

[Mattruby (Matthew Nash)]

mame (Yusuke Endoh) wrote in #note-3:

The behavior of 2.5.5 was wrong. Array#map yields each element, in this case, ['one', 'two'], an array of two elements. The lambda requires two arguments, but one array is passed, which should raise "wrong number of arguments".

You may want to use -> (ary) { ary[0] } instead of -> (one, two) { one }. Or you can use proc {|one, two| one }.

Ok, the strange thing is it works for a Hash, and i assumed that map treats hashes and multi dimensional arrays in the same way.
Thanks though