Bug #14639: Array#map and lambda arity regression

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: 2.4.1+
• Backport: 2.3: DONTNEED, 2.4: REQUIRED, 2.5: DONE

[lenwood (Paul Martensen)]

From ruby 2.4.1 onward the following script breaks (ArgumentError):

print_three = ->(a, b, c) { puts [a, b, c] }
arr = [[1, 2, 3]]

arr.map(&print_three)

This now requires explicit destructuring:

print_three = ->((a, b, c)) { puts [a, b, c] }

I guess this comes from a change in enum.c (line 45) from #9605 which seems to be similar.

While digging around I found https://bugs.ruby-lang.org/projects/ruby-trunk/repository/revisions/48193/diff that seems to address this very issue but I'm not sure.

If this is expected behavior feel free to disregard this.

First time posting to ruby trunk so I'm sorry If there is any Information missing.

[marcandre (Marc-Andre Lafortune)]

• Subject changed from No #to_ary destructuring when mapping with lambda to Array#map and lambda arity change

[marcandre (Marc-Andre Lafortune)]

• Subject changed from Array#map and lambda arity change to Array#map and lambda arity regression

Good checking.

Indeed, #9605 introduced lambda arity relaxation and this announced in the 2.2 NEWS.

Looks like a regression was introduced by #12705?

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Closed

Applied in changeset trunk|r63030.

---

array.c: yield blockarg in collect

• array.c (rb_ary_collect): yield in block argument semantics
  always to splat array elements to lambda, for the backward
  compatibility. [ruby-core:86362] [Bug #14639]

[nobu (Nobuyoshi Nakada)]

• Backport changed from 2.3: UNKNOWN, 2.4: UNKNOWN, 2.5: UNKNOWN to 2.3: DONTNEED, 2.4: REQUIRED, 2.5: REQUIRED

[lenwood (Paul Martensen)]

That was incredibly quick. Thanks @nobu (Nobuyoshi Nakada) and @marcandre (Marc-Andre Lafortune)! :)

[nagachika (Tomoyuki Chikanaga)]

• Backport changed from 2.3: DONTNEED, 2.4: REQUIRED, 2.5: REQUIRED to 2.3: DONTNEED, 2.4: REQUIRED, 2.5: DONE

ruby_2_5 r64996 merged revision(s) 63030.

[shyouhei (Shyouhei Urabe)]

• Related to Bug #15285: lambda return behavior regression from #14639 added