From: Dave Thomas <Dave@...>
Date: 2002-01-24T14:11:50+09:00
Subject: Re: Array.last Weirdness

Jesse Jones <jesjones@mindspring.com> writes:

> I'd expect the following code: 
> 
>    array = ["hello"]
>    array.last += " world"
>    puts array
> 
> to print "hello world", but instead I get errors like "undefined method
> `last=' for ["hello"]:Array (NameError)". This doesn't seem too good...

xxx += y is shorthand for   xxx = xxx + y.

When 'xxx' is the name of a variable, this makes sense. Take the value
in the variable xxx, invoke its '+' method (passing in y), and then
assign whatever comes back to 'xxx'

However,  array.last = array.last + y make less sense. What are you
assigning the result to? There's no variable there, just the method
call, array.last. Now Ruby's fairly clever here. It sees that you need
an lvalue method, and so looks for a method called 'last='. When it
can't find one, it gives up and reports the error. There's really
nothing else it can do.

However, rather than trying to assign to the string, you could use
methods in class String to append to the element in the array:

  a = ["hello"]
  a.last.concat "wor"
  a.last << "ld"


Regards


Dave