From: Per-erik Martin <lists@...>
Date: 2013-05-13T22:48:11+09:00
Subject: Re: Unexpected output from Array#<< method.

concat modifies the string:

irb(main):001:0> s = "foo"
"foo"
irb(main):002:0> s.concat("x")
"foox"
irb(main):003:0> s
"foox"

If you want to get the concatenation without modifying the string, use 
"+" instead.

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