Bug #15174: Sorting array of elements using "&:size" block, in which more than 1 element

• Status: Rejected
• Assignee: -
• Target version: -
• ruby -v: 2.5.1, 2.6.0-preview2
• Backport: 2.3: UNKNOWN, 2.4: UNKNOWN, 2.5: UNKNOWN

[Mr_Cartoon (Mr Cartoon)]

Example with ranges(first with what defined bug), but also tested on strings, symbols, integers
Good

[1..2].sort { |x| x.size }
[1..2, 4..5].sort { |x| x.size }
[1..2].sort(&:size)

Bad

[1..2, 4..5].sort(&:size)

Traceback (most recent call last):
4: from /home/sviat/.rvm/rubies/ruby-2.6.0-preview2/bin/irb:11:in <main>' 3: from (irb):3 2: from (irb):3:in sort'
1: from (irb):3:in `size'
ArgumentError (wrong number of arguments (given 1, expected 0))

Tested ruby versions: 2.5.1, 2.6.0-preview2

[jeremyevans0 (Jeremy Evans)]

You want sort_by, not sort:

[1..2, 4..5].sort_by(&:size)
# => [1..2, 4..5]

The difference in behavior between { |x| x.size } and (&:size) is due to how ruby handles Symbol#to_proc when multiple arguments are yielded. If a block yields multiple arguments, Symbol#to_proc is the equivalent of first_arg.send(symbol, *remaining_args), not first_arg.send(symbol) or [first_arg, *remaining_args].send(symbol). Example:

def b(*a)
  p [self, a]
  1
end

[1..2, 4..5].sort{|x| x.b}
# => [4..5, 1..2]
# output:
# [1..2, []]

[1..2, 4..5].sort(&:b)
# => [4..5, 1..2]
# output:
# [1..2, [4..5]]

Range#size does not take an argument, hence the ArgumentError when you are using sort(&:size) with an array of Range instances.

I believe this behavior is expected (see vm_yield_with_symbol in vm_insnhelper.c). However, a more experienced rubyist should probably confirm that.

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Rejected

An expected behavior.