From: Yukihiro Matsumoto <matz@...>
Date: 2011-11-03T19:49:10+09:00
Subject: [ruby-dev:44792] [ruby-trunk - Feature #5553][Feedback] A method for Hash that works differently depending on whether a key exists


Issue #5553 has been updated by Yukihiro Matsumoto.

Status changed from Open to Feedback

「fetchや[]を頻繁に呼びたくない」という意図は伝わらないでも無いですが、でもそれよりもif_keyメソッドのほうが嬉しい局面というのがあまり想像できません。単にメソッドでラップすればいいんじゃないですか？ 
正直、この例では全然嬉しくないと思います。もうちょっと人工的でない例だと嬉しさがイメージできるかもしれません。
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Feature #5553: A method for Hash that works differently depending on whether a key exists
http://redmine.ruby-lang.org/issues/5553

Author: Tsuyoshi Sawada
Status: Feedback
Priority: Normal
Assignee: 
Category: 
Target version: 


A method Hash#if_key(key, [default], &pr) which works like the following will be often used, and is useful.

    a = {morning: "おはよう", daytime: "こんにちは", evening: "こんばんは", nothing: nil}
    a.if_key(:morning){|str| "#{str}世界!"} #=> "おはよう世界!"
    a.if_key(:nothing){|str| "#{str}世界!"} #=> "世界!"
    a.if_key(:midnight){|str| "#{str}世界!"} #=> nil
    a.if_key(:nothing, "どうも"){|str| "#{str}世界!"} #=> "どうも"

That is, when `key' exists, then the corresponding value will be passed to `pr'. Otherwise, the given `default' or the implicit default will be returned.




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