pgfkeys: allowing one key to activate another key

Question

I have two custom keys: key1, which is boolean; and key2, which accepts a value. The idea is that key1 activates a feature, and key2 customizes the feature. However, if key2 is used, I want key1 set to true automatically. So:

\tikzset{key2=3.5cm)

and

\tikzset{key1=true, key2=3.5cm}

should have the same effect.

All I need help with is making it so that key1 is automatically set to true when key2 is set to any value.

Answer 1

Name your original key2 to @key2 or any other internal name and define key2 as follows:

\tikzset{key2/.style={key1=true, @key2={#1}})

This will pass the value to the internal key and also switch the boolean key on.