The box <> is a placeholder for something not (yet) fully specified.
- In array declaration
Declare an array type with bounds known only at runtime.
- a type that has unknown discriminants
- Generic declaration of a discrete type
It means that T must be a discrete type: either an enumeration, a range, or a modular type.
- component association in Ada 2005
- partial parameterization of generics in Ada 2005