ruby-dev

At Thu, 26 Feb 2009 14:52:05 +0900,
Yugui wrote:
> On 2/26/09 3:33 AM, Yukihiro Matsumoto wrote:
> > 検討事項は
> >   * 名前。今回はnested loopということでnloopという名前で実装
> >     したが、もっと適切な名前があるかもしれない。妙な短縮形よ
> >     りも長くても記述的な名前を好む人も多いかも。Ruby(というか
> >     私)は前者を好む傾向はあるけど
>
> Array#productがカルテシアン積なので、それに合わせてEnumerator#productで
>
> nphi.product(ntheta).each {} や

　インスタンスメソッド形式は、(Array#zip 等でも感じることですが)
3つ以上あるときに、本来対等な関係にも関わらず

    v1.product(v2, v3)

とか

    v, *vs = *vectors
    v.product(*vs)

と「主」を立てないといけないのがどうも気に入らないんですよね。


　その点、こちらは記法としては美しいと思います:

> (nphi * ntheta).each {}

しかし、 Enumerable の演算子とするのは現実的に不可能(Array#* 等と
衝突する)なので、結局は各オペランドを to_enum (each) してから演算
せざるを得ず、演算するため(だけ)にわざわざ変換するというのはやや
使い勝手に欠ける印象があります。

　Enumerator のクラスメソッドで実装するのはどうでしょうか。

class << Enumerator
  def product(*enums)
    return to_enum(__method__, *enums) unless block_given?

    return nil if enums.empty?

    e, *es = *enums

    if es.empty?
      e.each { |x|
        yield [x]
      }
    else
      e.each { |x|
        product(*es) { |xs|
          yield [x, *xs]
        }
      }
    end

    nil
  end

  alias nest product
end

Enumerator.nest(1..3, 'a'..'c', [true, false]) { |x|
  p x
}

　もし簡潔さにこだわるなら、 {Class,Module}#* は今後ないだろうと
見切って alias * product してしまえば

Enumerator.*(1..3, 'a'..'c', [true, false]) { |x|
  p x
}

と書けますね…。

　ただ、演算子を導入し始めると、類推や一貫性への期待から次々と
新しい提案がなされ、利便性と理論的整合性の間で苦しみ続けることに
なるのではないかという懸念も持っています。
(cf. Feature #709 [ruby-core:19681])


　なお、他に思いついたクラスメソッドは

    Enumerator.transpose (synchronize)
    Enumerator.join (<< or +)

などです。(前者は generator ライブラリの SyncEnumerator と同等)

--
Akinori MUSHA / http://akinori.org/

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[#37874] Symbol as String for C — arton <artonx@...>

[#37880] [FEATURE:trunk] Readline.completion_proc = nil を許可する。 — Takao Kouji <[email protected]>

[#37882] test_etc.rb の修正提案 — Tomoyuki Chikanaga <chikanag@...>

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[#37887] [Bug #1097](Rejected) Ruby 1.9.1 における sqlite3-ruby のインストール時のエラー — Usaku NAKAMURA <redmine@...>

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[#37891] Ruby 1.9.1-p0 on NetBSD — Takahiro Kambe <taca@...>

[#37892] 配列の重複検出用Hashの使いまわし — wanabe <s.wanabe@...>

[#37896] [Bug #1104] TZ and Time.now — Nobuhiro IMAI <redmine@...>

[#37898] [Bug #1105] Ruby1.9でのrescue節の例外ハンドラのマッチの処理 — Tatsuji Kawai <redmine@...>

[#37906] Buffering or OpenSSL::Buffering — Kazuhiro NISHIYAMA <zn@...>

[#37910] [Bug:1.9] lack consistency in hash iteration — Yusuke ENDOH <mame@...>

[#37918] [BUG: 1.9] encoding warning — SASADA Koichi <ko1@...>

[#37919] RDoc::Markup::ToHtmlCrossref dosen't recognize filepath including '-' — Tomoyuki Chikanaga <chikanag@...>

[#37920] [Bug #1111] -E and -K on shbang — Usaku NAKAMURA <redmine@...>

[#37921] [Feature:trunk] with_index_from — Yusuke ENDOH <mame@...>

[#37926] [Bug #1115] $SAFE=1でのrequireがSecurityErrorになる — Kazuhiro NISHIYAMA <redmine@...>

[#37930] -r時のdefault_external — "U.Nakamura" <usa@...>

[#37934] [BUG] rb_thread_create_timer_thread: return non-zero (11) — Tanaka Akira <akr@...>

[#37935] test_imaps_post_connection_check test failure — Tanaka Akira <akr@...>

[#37936] zombie processes by drb tests — Tanaka Akira <akr@...>

[#37939] io.set_encoding("UTF-8", "UTF-8") でエラー — Hiroshi Ichikawa <gimite@...>

[#37940] [Bug #1129] IO.binread(Pathname(...)) dumps core — Sakuro OZAWA <redmine@...>

[#37947] Re: [ruby-list:45859] Re: patch for Complex#sqrt in lib/cmath.rb of ruby-1.9.1-p0 — Tadayoshi Funaba <tadf@...>

[#37950] [Bug:1.9] compile error on win32ole with Mingw of MacPorts — 中田 伸悦 <nobu@...>

[#37952] [Feature #1133] Pathname.binread — Sakuro OZAWA <redmine@...>

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[#37968] 1.9.1-p0 の Net::HTTP#get の第 2 引数 — zunda <zunda616e@...>

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[#37975] [Bug #1148] CGI::prettyの正規表現の改良 — Takeyuki Fujioka <redmine@...>

[#37977] trunk が compile error します — nagachika <nagachika00@...>

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[#37980] Re: [ruby-changes:10687] Ruby:r22250 (trunk): * iseq.c (simple_default_value): allow plain strings as default — SASADA Koichi <ko1@...>

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[#37993] Re: [ruby-core:22028] Re: 1.8.7 Specifics — Urabe Shyouhei <shyouhei@...>

[#37995] Add POSTARG support to rb_scan_args() — Akinori MUSHA <akinori.musha@...>

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[#37998] [Feature:1.9] {Array,Enumerable}#uniq_by, #uniq_by! — Nobuyoshi Nakada <nobu@...>

[#37999] [Feature:1.9] Etc.each_passwd, each_group — Nobuyoshi Nakada <nobu@...>

[#38005] Is URI.decode() broken? — MOROHASHI Kyosuke <moronatural@...>

[#38007] [Feature #1159] StringScanner に文字ベースでのインデックスを返すメソッドがほしい — Akira Matsuda <redmine@...>

[#38018] circular require in openssl — Tanaka Akira <akr@...>

[#38020] [Bug #1163] gem_prelude raise NoMethodError if require uninsalled gem with version. — Kyosuke MOROHASHI <redmine@...>

[#38021] 無名クラス中で定義された定数の扱いに付いて — MOROHASHI Kyosuke <moronatural@...>

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[#38048] Add option hash support to rb_scan_args() — "Akinori MUSHA" <knu@...>

[#38049] [Bug #1175] File.expand_path("~user") dose not work — Tomoyuki Chikanaga <redmine@...>

[#38050] indentation check and coverage for toplevel do not work — Yusuke ENDOH <mame@...>

[#38052] mkmf.rb の C++ 対応 — "KISHIMOTO, Makoto" <[email protected]>

[#38054] build breakage with NO_WAITPID macro — shinichiro.h <shinichiro.hamaji@...>

[#38055] signal is ignored after Process.daemon — Yusuke ENDOH <mame@...>

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[#38060] [Bug:1.9] thread switch when heavy load — Tanaka Akira <akr@...>

[#38063] [Bug #1191] Net::IMAP.encode_utf7 bug? — Kengo Matsuyama <redmine@...>

[#38065] Re: [ruby-cvs:29711] Ruby:r22493 (trunk): * lib/pathname.rb (Pathname#binread): added. — Tanaka Akira <akr@...>

[#38067] Re: [ruby-cvs:29304] Ruby:r22086 (trunk): * ruby.c (process_options): set initial default_external before -r. — "Yugui (Yuki Sonoda)" <yugui@...>

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[#38075] [Bug #1198] corrupted iteratoin during "enum_for :inject" — Shyouhei Urabe <redmine@...>

[#38079] [Bug:trunk] duplicate when clauses raise strange exception — Yusuke ENDOH <mame@...>

[#38080] [Feature:trunk] nested loop construct — Yukihiro Matsumoto <matz@...>

[#38086] [Bug: 1.8] generator causes abort — SASADA Koichi <ko1@...>

[#38087] [Bug #1215] irb doesn't finish evaluate on !false => false — Nobuhiro IMAI <redmine@...>

[#38091] mswin32's nan_test is broken by r22579 — "U.Nakamura" <usa@...>

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[#38098] ブロック引数と括弧・引数なしsuper — Shugo Maeda <shugo@...>

[#38101] [Bug #1221](Closed) [PATCH] load がディレクトリを読み込もうとしてエラー — Nobuyoshi Nakada <redmine@...>

[#38105] ruby in non-existing directory — Tanaka Akira <akr@...>

[#38106] test/ruby/test_m17n.rb dumps core — Yukihiro Matsumoto <matz@...>

[ruby-dev:38095] Re: [Feature:trunk] nested loop construct

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[#37950] [Bug:1.9] compile error on win32ole with Mingw of MacPorts — 中田伸悦 <nobu@...>