3.2 ADT details

In order to support the features describe in the previous section, it is best to use an ADT architecture. Let us describe this architecture in a bottom up fashion.

Data member definition. A data member definition describes a data member in a record type. It has the following interface:

• initialize: creates and initializes a data member definition. The name of the data member definition should be supplied at this point. If data members are typed, the type should be specified at this point. The same logic applies the any default value for a data member definition.
• getName: retrieves the name of the data member definition. This operation is useful when the containing record type needs to list all of its data members, or to search for one based on name.
• getType: retrieves the type of a data member definition.
• getDefaultValue: retrieves the default value of a data member definition.

Record type. A record type is analogous to a named struct in C, or a class in C++ without methods. It has the following interface:

• initialize: creates and initializes a record type. The name of the record type should supplied at this point.
• addDataMemberDefn: add a data member definition to a record type.
• removeDataMemberDefn: removes a data member definition from a record type.
• lookupDataMemberDefn: looks up a data member definition from a record type based on name. Returns a data member definition.
• getDataMemberDefnNames: returns a list of names of data member definitions.
• createInstance: creates and initializes a record (instance) from a record type.

Data member. A data member is a part of a record (instance). A data member has a particular value, and it must correspond to a data member definition. Its interface is as follows:

• initialize: creates and initializes a data member. The parameter should include a data member definition so that the data member can acquire a default value.
• setValue: sets the value of a data member.
• getValue: retrieves the value of a data member.
• getDefinition: retrieves the data member definition that corresponds to a data member.

Record (instance). A record (instance) is an actual record with its own state. It has the following interface:

• initialize: creates and initializes a record. The parameter should include a record type to indicate how to create this record.
• getRecordType: retrieves the record type of a record.
• getDataMemberValue: retrieves the value of a data member by name.
• setDataMemberValue: sets the value of a data member by name.

To make things a little easier to understand, here is an example using the built-in struct construct in C.

struct X // record type, name is X
{
  int i; // data member defn, name is i, type is int
  float f; // data member defn, name is f, type is float
};

{
  X myX; // record (instance) myX
  myX.i = 0; // record->setDataMember
  printf("%f\n",myX.f); // record->getDataMember
}