How to dynamically call accessor methods in Ruby

Regardless of whether it's good practice or not, how can I dynamically call accessor methods in Ruby?

Here's an example class:

class Test_Class
attr_accessor :a, :b
end

I can use the Object.send method to read the variable...

instance.a = "value"
puts( instance.send( "a" ) )
# => value

But I'm having a hard time trying to write to it. These throw "wrong number of arguments (1 for 0) (ArgumentError)"

instance.send("a", "value")
and

instance.method("a").call("value")

Please help me StackOverflow!

You can also directly access instance variables of an object using `instance_variable_*` functions:

instance = Test_Class.new # => #<Test_Class:0x12b3b84>

# instance variables are lazily created after first use of setter,
# so for now instance variables list is empty:
instance.instance_variables # => []

instance.instance_variable_set(:@a, 123) # => 123
instance.a # => 123
instance.instance_variables # => ["@a"]
instance.instance_variable_get("@a") # => 123

I am not a ruby expert, but I think that you could do:

instance.send("a=", "value")