Constraint subtype

Subtype constraints a supertype can introduce attributes that apply to several subtypes each subtype imposes specific constraints on the attributes. An example is illustrated in Section 3.7, Subtypes and Type Extension. 

Sometimes a state chart is deliberately vague about the outcome of an action. The reason is usually to allow subtypes to make different choices, within broad constaints given by the supertype, or simply to define a minimal partial constraint. 

In order to ]udge whether the overall galactic WR distribution poses constraints on subtype evolution, we have plotted in Fig. 1 the WR galactocentric distances R (based on Rg - 8.5 kpc) versus WR subtype. This was performed earlier by Hidayat et al-(1982. Paper I). but with the improved data base we find as more pronounced trend in Fig. 1 that the WC stars show a clear preference to have later subtypes at smaller distances from the center. WN2-5 stars are only present beyond R 6 kpc, while WN6-8 stars are present at practically all observable galactocentric distances. 

All of these constraints are ensured by the generic graph transformation shown in Fig. 5.61 to instantiate a new node for a given subtype of the node class Entity. Relationships between entities are instantiated analogously. 

Each identifier is the name of a port in the design. It is treated as a signal. The constraint, if any, applied to the type or subtype must be static. It may contain generics defined in a preceding generic statement. The default initial value expression of the port is ignored by the synthesizer. 

A restriction placed on the range of values that a given type may take is called a constraint A subtype is any type with a constraint. Declaring an object as a type subjected to a constraint is equivalent to declaring a subtype. An unconstrained type does not have any restriction placed on the range of values that an object of that type may take. The four classes of types are ... 

Once a subtype has been declared it can itself be used as the base type for further subtype declarations. Any two subtypes that are ultimately derived from the same unconstrained type can be mixed in one expression. However, it is important to ensure that the range constraints on both sides of an assignment statement are matched. For example, if two integer subtypes and two signals are defined as follows ... 

If a constraint is not applied the subtype is exactly the same as the. type or subt) e from whid it is being declared. 

The form of the constraint expression is dependent upon the type or subtype from which the subtype is being declared. The following examples illustrate range constraints ... 

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