From: Josh Cheek <josh.cheek@...>
Date: 2013-04-02T20:03:40+09:00
Subject: Re: Ruby Gotchas presentation slides

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On Sun, Mar 31, 2013 at 1:36 AM, Josh Cheek <josh.cheek@gmail.com> wrote:

>
> The example for local var in the block seems too contrived. It's only ever
> hit me when I tried to do something like `.each{ |i| sum ||= 0; sum += i }`
> in the loop, in which case it always gets set to zero.
>
>
There's also the opposite side of this, which is that a var in a for loop
doesn't open a new scope on each invocation, which can be confusing because
all iterations are using the same variable.

blocks = []
1.upto(5) { |i| blocks << lambda { i } }
blocks.map &:call # => [1, 2, 3, 4, 5]

blocks = []
for i in 1..5; blocks << lambda { i } end
blocks.map &:call # => [5, 5, 5, 5, 5]


Or could cause you to override a variable you meant to shadow

var = 100

1.upto(10) { |var| }
var # => 100

for var in 1..10; end
var # => 10


Might be too nuanced, but if you don't understand the object model, it
might be unclear why include doesn't override your instance methods.

module A
  def meth
    'A#meth'
  end
end

class B
  def meth
    'B#meth'
  end

  include A
end

B.new.meth # => "B#meth"

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<div dir=3D"ltr">On Sun, Mar 31, 2013 at 1:36 AM, Josh Cheek <span dir=3D"l=
tr">&lt;<a href=3D"mailto:josh.cheek@gmail.com" target=3D"_blank">josh.chee=
k@gmail.com</a>&gt;</span> wrote:<br><div class=3D"gmail_extra"><div class=
=3D"gmail_quote">
<blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-=
left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;p=
adding-left:1ex"><div dir=3D"ltr"><div class=3D"im"><div><br></div></div><d=
iv class=3D"gmail_extra">
<div>The example for local var in the block seems too contrived. It&#39;s o=
nly ever hit me when I tried to do something like `.each{ |i| sum ||=3D 0; =
sum +=3D i }` in the loop, in which case it always gets set to zero.</div>
<div><br></div></div></div></blockquote><div><br></div><div style>There&#39=
;s also the opposite side of this, which is that a var in a for loop doesn&=
#39;t open a new scope on each invocation, which can be confusing because a=
ll iterations are using the same variable.</div>
<div><br></div><div><div><div>blocks =3D []</div><div>1.upto(5) { |i| block=
s &lt;&lt; lambda { i } }</div><div>blocks.map &amp;:call # =3D&gt; [1, 2, =
3, 4, 5]</div></div></div><div><br></div><div><div><div>blocks =3D []</div>=
<div>
for i in 1..5; blocks &lt;&lt; lambda { i } end</div><div>blocks.map &amp;:=
call # =3D&gt; [5, 5, 5, 5, 5]</div></div></div><div><br></div><div><br></d=
iv><div style>Or could cause you to override a variable you meant to shadow=
</div>
<div style><br></div><div style><div>var =3D 100</div><div><br></div><div>1=
.upto(10) { |var| }</div><div>var # =3D&gt; 100</div><div><br></div><div>fo=
r var in 1..10; end</div><div>var # =3D&gt; 10</div><div><br></div><div><br=
></div>
<div style>Might be too nuanced, but if you don&#39;t understand the object=
 model, it might be unclear why include doesn&#39;t override your instance =
methods.</div><div style><br></div><div style><div>module A</div><div>=A0 d=
ef meth</div>
<div>=A0 =A0 &#39;A#meth&#39;</div><div>=A0 end</div><div>end</div><div><br=
></div><div>class B</div><div>=A0 def meth</div><div>=A0 =A0 &#39;B#meth&#3=
9;</div><div>=A0 end</div><div><br></div><div>=A0 include A<br></div><div>e=
nd</div><div>
<br></div><div>B.new.meth # =3D&gt; &quot;B#meth&quot;</div><div><br></div>=
</div></div></div></div></div>

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