From: "月忧茗" <yueyoum@...>
Date: 2012-10-27T23:26:57+09:00
Subject: Newbie, questions about === expression

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Hi,

I'm learning ruby this days.
And I followed this docs:  http://www.ruby-doc.org/docs/ProgrammingRuby/


Now, I have some questions about ===  expression


irb(main):138:0> case 1
irb(main):139:1> when 1..10 then 'in'
irb(main):140:1> else 'not in'
irb(main):141:1> end

obviously, the result is 'in'

In the docs, there are an explanation:
*case operates by comparing the target (the expression after the keyword
case) with each of the comparison expressions after the when keywords. This
test is done using comparison === target. As long as a class defines
meaningful semantics for === (and all the built-in classes do), objects of
that class can be used in case expressions. *


But,  when I type this,  why throw an error ?

irb(main):149:0> 1..10 === 1
ArgumentError: bad value for range
    from (irb):149
    from /opt/ruby-1.9.3/bin/irb:12:in `<main>'



Thanks.

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Hi, <br><br>I&#39;m learning ruby this days.<br>And I followed this docs:=
=C2=A0 <a href=3D"http://www.ruby-doc.org/docs/ProgrammingRuby/">http://www=
.ruby-doc.org/docs/ProgrammingRuby/</a><br><br><br>Now, I have some questio=
ns about =3D=3D=3D=C2=A0 expression<br>
<br><br>irb(main):138:0&gt; case 1<br>irb(main):139:1&gt; when 1..10 then &=
#39;in&#39;<br>irb(main):140:1&gt; else &#39;not in&#39;<br>irb(main):141:1=
&gt; end<br><br>obviously, the result is &#39;in&#39;<br><br>In the docs, t=
here are an explanation:=C2=A0 <br>
<b><code>case</code> operates by comparing the target (the expression after=
 the
keyword <code>case</code>) with each of the comparison expressions after th=
e
<code>when</code> keywords.  This test is done using
<em>comparison</em>=C2=A0<code>=3D=3D=3D</code>=C2=A0<em>target</em>.=20
As long as a class defines
meaningful semantics for <code>=3D=3D=3D</code> (and all the built-in class=
es do),
objects of that class can be used in case expressions.
</b><br><br><br>But,=C2=A0 when I type this,=C2=A0 why throw an error ?<br>=
<br>irb(main):149:0&gt; 1..10 =3D=3D=3D 1<br>ArgumentError: bad value for r=
ange<br>=C2=A0=C2=A0=C2=A0 from (irb):149<br>=C2=A0=C2=A0=C2=A0 from /opt/r=
uby-1.9.3/bin/irb:12:in `&lt;main&gt;&#39;<br>
<br><br><br>Thanks.<br>

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