Ruby String Interpolation Weirdness

I think it is interesting some of the variations on the standard Ruby string interpolation.

Basics.

Generally you can interpolate double quote (") delimited strings with #{...} like so:

value = "String"
"This is a #{ value }!"

With single quote (') strings, you can't interpolate, you must use concatenation:

value = 'String'
'This is also a ' + value + '!'

Okay, so that's pretty straight forward.

Weirdness.

What ruby lets you do however, is interpolate some special variables in a different way: using only #.

$globals and @instance_variables

Globals and instance variables can be interpolated with or without the curly braces.

# Global Var
$foo = "bar"

"#{$foo} #$foo $foo"
#=> "bar bar $foo"

# Instance Var
@foo = "bar"

"#{@foo} #@foo @foo"
#=> "bar bar @foo"

Just for clarity this doesn't work with constants or local variables:

foo = FOO = "bar"

"#{foo} #foo foo #{FOO} #FOO FOO"
#=> "bar #foo foo bar #FOO FOO" 

Nothing earth shattering, just a litle bit weird.

This was originally posted as a Github Gist .