API and logic for optional or not-optional members?

[metaperl]

1. If defining a member is optional what syntax is used?
2. If a member must be defined when constructing an instance, what syntax specifies this?
3. If a member is optional and no default value has been specified what happens?

[MatthieuDartiailh]

Atom does not generate automatically an __init__ so by default you can always create an instance. Extending the API to generate
meaningful init by default is on my mind but I do not have a concrete plan yet.