From: Peter <Peter.Vanbroekhoven@...>
Date: 2003-09-17T07:12:16+09:00
Subject: #{} and \" don't like each other

From the Programming Ruby book:
<quote>
  In addition, you can substitute the value of any Ruby expression
  into a string using the sequence #{ expr }.
</quote>

Up to about an hour ago, I never doubted this statement. I've stumbled
upon the following example which is not accepted by ruby. The following
piece of code works perfectly, as to be expected:

  name = "peter"
  temp = "name=\"" + name + "\""
  print "<user #{temp}></user>"

This prints exactly what I want it to print, namely:

  <user name="peter" ></user>

One would expect that substituting the RHS of the assignment to temp for
temp in the third statement, would work as well:

  name = "peter"
  print "<user #{"name=\"" + name + "\""}></user>"

Type this in at the ruby prompt and you'll soon notice that it gives you
the following prompt and not the expected output as above:

  irb(main):003:-1/

Note the -1 in the prompt, meaning ruby managed to get above the toplevel.

Ruby just keeps waiting for input, and I can type anything but ruby will
stay in this state until I type a / and then unhappily states this:

  (irb):2: warning: escaped terminator '"' inside string interpolation
  SyntaxError: compile error
  (irb):3: unterminated string meets end of file
  (irb):3: syntax error
          from (irb):3

Anyway, what happens is that the escaped quotes are misinterpreted since
the problem is gone when I leave them out. The effect is that the slash in
</user> is interpreted as the start of a regular expression. This can only
be if ruby thinks it's not part of a string string, which was clearly not
my intention.

Can someone please tell me whether this is a bug, or otherwise why I
shouldn't have done the above.

Note: I'm using version 1.8.0 of ruby, don't know if the trueness of the
above statement from Programming Ruby changed as the ruby version changed.

Thanks,
Peter