```Issue #9782 has been updated by Yusuke Endoh.

Status changed from Open to Rejected

Array#bsearch is binary search; it works correctly *only when* the array is sorted.
In other words, "ary.map { cond }" must return [false, false, ..., false, true, true, ..., true] if you want to use "ary.bsearch { cond }".

> [{a:1, b:2}, {a:3, b:4}].bsearch{|x| x[:a] == 1}

NG, [{a:1, b:2}, {a:3, b:4}].map {|x| x[:a] == 1 } returns [true, false].

> [{a:3, b:4}, {a:1, b:2}].bsearch{|x| x[:a] == 1}

OK, [{a:3, b:4}, {a:1, b:2}].map {|x| x[:a] == 1} returns [false, true].

> [{a:3, b:4}, {a:1, b:2}].bsearch{|x| x[:a] == 3}

NG, [{a:3, b:4}, {a:1, b:2}].map {|x| x[:a] == 3} returns [true, false].

> [{a:3, b:4}, {a:1, b:2}].bsearch{|x| x[:b] == 4}

NG, [{a:3, b:4}, {a:1, b:2}].map {|x| x[:b] == 4} returns [true, false].

> [{a:3, b:4}, {a:1, b:2}, {a:3, b:5}].bsearch{|x| x[:a] == 3}

NG, [{a:3, b:4}, {a:1, b:2}, {a:3, b:5}].map {|x| x[:a] == 3} returns [true, false, true].

You should use Enumerable#find for your cases.

--
Yusuke Endoh <mame / tsg.ne.jp>

----------------------------------------
Bug #9782: Array#bsearch skip first match while using block with complex condition
https://bugs.ruby-lang.org/issues/9782#change-46362

* Author: Valentin Syrovatskiy
* Status: Rejected
* Priority: Normal
* Assignee:
* Category:
* Target version:
* ruby -v: ruby 2.1.1p76 (2014-02-24 revision 45161) [x86_64-linux]
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN
----------------------------------------
Description: Array#bsearch cannot find first match when using block with condition by hash key.

Example:
\$ irb
2.1.1 :001 > [{a:1, b:2}, {a:3, b:4}].bsearch{|x| x[:a] == 1}
=> nil
(WRONG, expected {a:1, b:2})
2.1.1 :002 > [{a:3, b:4}, {a:1, b:2}].bsearch{|x| x[:a] == 1}
=> {:a=>1, :b=>2}
(Correct, successfully find same item if it in second position)
2.1.1 :003 > [{a:3, b:4}, {a:1, b:2}].bsearch{|x| x[:a] == 3}
=> nil
(WRONG, expected {a:3, b:4})
2.1.1 :004 > [{a:3, b:4}, {a:1, b:2}].bsearch{|x| x[:b] == 4}
=> nil
(WRONG, expected {a:3, b:4})
2.1.1 :005 > [{a:3, b:4}, {a:1, b:2}, {a:3, b:5}].bsearch{|x| x[:a] == 3}
=> {:a=>3, :b=>5}
(WRONG, expected {a:3, b:4})

Environment:
\$ rvm info
ruby-2.1.1:
system:
uname:       "Linux magic 3.14.2-031402-generic #201404262053 SMP Sun Apr 27 00:54:28 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux"
system:      "ubuntu/12.04/x86_64"
rvm:
version:      "rvm 1.25.24 (stable) ..."
ruby:
interpreter:  "ruby"
version:      "2.1.1p76"
date:         "2014-02-24"
platform:     "x86_64-linux"
patchlevel:   "2014-02-24 revision 45161"
full_version: "ruby 2.1.1p76 (2014-02-24 revision 45161) [x86_64-linux]"

Bug also can be reproduced with linux ruby 2.0.0 (ruby 2.0.0p451 (2014-02-24 revision 45167) [x86_64-linux]) and windows ruby 2.0.0 (ruby 2.0.0p451 (2014-02-24) [i386-mingw32]). Other versions and platforms were not tested.

--
https://bugs.ruby-lang.org/
```