Why can I not concatenate two strings and assign them to a symbol?

. . . as in this example:

helloworld.rb:1: syntax error, unexpected '=', expecting $end
:helloworld = "hello ".concat("world")

I thought if I use concat I'm modifying the string "hello " and adding "world" to it and then ultimately assigning the resulting string - "hello world" - to the :helloworld symbol on the left side of the equals sign. I thought that would be legal, just as if I had written:

:helloworld = "hello world"

oh, wait, that doesn't work either. (scratches head).

From stackoverflow

• Well, yeah. You can't assign to symbols. Do you mean something like:

  foo = { :helloworld => "hello ".concat("world") }
  

  ?

• Ruby symbols cannot have values assigned to them since they represent a canonical value. If you want to build a symbol from a string, you can use "hello ".concat("world").to_sym.

  dbarker : There are a couple other options. :"hello world" is the most direct, but if the symbol is unknown until runtime, you could store it in a var: foo = "hello ".concat("world").to_sym.

• symbols are confusing when coming from languages that don't have anything like them. You can't assign to symbols, that's not what they're for.

  Here are a couple of examples that may help explain it.

  5.times do |i|
    # a new string is created in each iteration of the loop
    puts "my string".object_id
  
    # there is only ever one symbol for each possible value
    # so a new object is not created during each iteration
    puts :my_symbol.object_id
  
    # this often makes a difference when you're using them for things like hash keys
    #some_method(:name => 'bob')
    #some_method('name' => 'bob')
  end
  

  The other big difference is that a symbol comparison is simply a pointer comparison.

• Perhaps what you're actually looking for is a constant? They can be dynamically generated, referred to later, and you get a warning if you try to reassign one.

  >> HELLO_WORLD = "hello ".concat("world")
  => "hello world"
  >> HELLO_WORLD = "foo"
  (irb):3: warning: already initialized constant HELLO_WORLD
  => "foo"
  

• Try this:

  :"hello world"