The Scalar Types

Besides the types used for container management, that are described separately in Section , the following external and enumeration types are declared in the schema knl:

extern void (0);

extern sos_Int (4);
extern sos_Bool (1);
extern sos_Char (1);
extern sos_Cstring (4);
extern sos_Pointer (4);

enum   sos_Bool {FALSE, TRUE};
enum   sos_Eq_kind {EQ_STRONG, EQ_WEAK};
enum   sos_Comp_result {CMP_LESS, CMP_EQUAL, CMP_GREATER};

The type sos_Int represents integer numbers. The numbers supported by the kernel are restricted to a length of four bytes (whereby a two's-complement form is used).

The type sos_Char represents one-byte ASCII characters; the type sos_Cstring is intended to hold a pointer to a successive number of sos_Char objects, whose end is indicated by the ASCII control character NUL, whereas the type sos_Pointer is intended to hold arbitrary pointers to main memory.

The enumeration type sos_Bool represents the boolean truth values. The enumeration type sos_Eq_kind is presumably mostly used as argument type in calls of the predefined method equal (see Section ). The remaining enumeration type sos_Comp_result can be used as the return value of comparison operations (see e.g. sos_Ordered_object).

Objects of the predefined scalar types and all enumeration types are stored in the SOS system in an exactly defined, machine and language independent way.They can be used by applications written in different languages and running on different machines.

Scalar types are no class types, therefore no instances of a scalar type can be created and no application specific function methods can be defined for them. Objects of scalar types lie on the boundary between SOS and a host programming language. This is examplified by the fact that there are two representations of these objects:

• A representation in the host language obtained by mapping the scalar type to a type in the respective programming language. This representation can be manipulated as defined in the respective language.
• An object representation which acts like an instance of a subtype of class sos_Scalar_object, i.e. this representation can be used anywhere, where instances of sos_Scalar_object may appear.