<p>How can I add an instance variable to a defined class at <b>runtime</b>, and later get and set its value from outside of the class?</p>

<p>I'm looking for a metaprogramming solution that allows me to modify the class instance at runtime instead of modifying the source code that originally defined the class.  A few of the solutions explain how to declare instance variables in the class definitions, but that is not what I am asking about.  </p>

Ruby provides methods for this,
```
instance_variable_get
```
and
```
instance_variable_set
```
. (
docs
)
You can create and assign a new instance variables like this:
```
```
>> foo = Object.new
=> #<Object:0x2aaaaaacc400>

>> foo.instance_variable_set(:@bar, "baz")
=> "baz"

>> foo.inspect
=> #<Object:0x2aaaaaacc400 @bar=\"baz\">
```
```