Iterate EffectiveModel with visitor pattern

User Story:

The EffectiveModel graph contains nodes of arbitrary type. How can a consumer iterate the nodes without loosing type information?

Considered Alternatives

• Use instanceof
• Use double dispatch of visitor pattern

Decision Outcome

• Chosen Alternative: Use double dispatch of visitor pattern

Comes out best - see above.

Pros and Cons of the Alternatives

Use instance

Use a combination of instanceof and switch/if statements whenever you want to iterate the nodes.

if (node instanceof WebServer){
    doSomething(node)
}

• + straightforward
• - really ugly, boilerplate

Use double dispatch of visitor pattern

• + clean
• + extendable with use of java 8 default methods in interfaces
• + code reuse is easier
• - makes architecture a bit more complex
• - boilerplate in tosca elements: every class needs an accept() method