Ruby Language Introspection View Global and Local Variables
Example
The Kernel exposes methods for getting the list of global_variables and local_variables:
cats = 42
$demo = "in progress"
p global_variables.sort
#=> [:$!, :$", :$$, :$&, :$', :$*, :$+, :$,, :$-0, :$-F, :$-I, :$-K, :$-W, :$-a,
#=> :$-d, :$-i, :$-l, :$-p, :$-v, :$-w, :$., :$/, :$0, :$1, :$2, :$3, :$4, :$5,
#=> :$6, :$7, :$8, :$9, :$:, :$;, :$<, :$=, :$>, :$?, :$@, :$DEBUG, :$FILENAME,
#=> :$KCODE, :$LOADED_FEATURES, :$LOAD_PATH, :$PROGRAM_NAME, :$SAFE, :$VERBOSE,
#=> :$\, :$_, :$`, :$binding, :$demo, :$stderr, :$stdin, :$stdout, :$~]
p local_variables
#=> [:cats]
Unlike instance variables there are no methods specifically for getting, setting, or removing global or local variables. Looking for such functionality is usually a sign that your code should be rewritten to use a Hash to store the values. However, if you must modify global or local variables by name, you can use eval with a string:
var = "$demo"
eval(var) #=> "in progress"
eval("#{var} = 17")
p $demo #=> 17
By default, eval will evaluate your variables in the current scope. To evaluate local variables in a different scope, you must capture the binding where the local variables exist.
def local_variable_get(name, bound=nil)
foo = :inside
eval(name,bound)
end
def test_1
foo = :outside
p local_variable_get("foo")
end
def test_2
foo = :outside
p local_variable_get("foo",binding)
end
test_1 #=> :inside
test_2 #=> :outside
In the above, test_1 did not pass a binding to local_variable_get, and so the eval was executed within the context of that method, where a local variable named foo was set to :inside.
