1. Complex Data Types
One very important measure of the “goodness” of a PL is the capability of its data types to model the problem space variables
Design issues for all data types
what is the syntax of references to variables?
what operations are defined and how are they specified?
Compilers use descriptors to maintain information about instances of types in a program
actually part of the symbol table
what’s needed in descriptor depends on particular type
when the descriptor is needed depends on the kind of type checking required
static, compile time only
dynamic, run-time as well

2. Primitive types
Numeric
Boolean
Character strings
Ordinal

3. Numeric Types
Range and Precision
Integer
Real
Decimal

4. Boolean

5. Character string

6. Character String Issues
Primitive or not
Snobol, Java primitive
Ada, F77, F90, Basic “somewhat” primitive
Pascal, C, C++ not primitive
Static or dynamic
Or limited length dynamic
Operations

7. Strings (continued) Evaluation Implementation aid to writability
as a primitive type with static length, they are inexpensive to provide--why not have them?
dynamic length is nice, but is it worth the expense?
Implementation
static length - compile-time descriptor
limited dynamic length - may need a run-time descriptor for length (but not in C and C++)
dynamic length - need run-time descriptor; allocation/deallocation is the biggest problem

8. Ordinal
Enumeration
Subrange

9. Arrays

10. Arrays Definition Mapping Memory allocation Slices Associative arrays
Row major or column major
Memory allocation
Static
Fixed stack dynamic
Stack dynamic
Heap dynamic
Slices
Associative arrays
Operations

11. Records

12. Records Definition Mapping Operations Faster than array subscripts
Elliptical references (COBOL, PL/I)
Operations
Move corresponding

13. Unions

14. Unions Definition Type checking? Useful but dangerous Not in Java
Ada yes, others no
Useful but dangerous

15. Sets
Pascal, Java

16. Pointers

17. Pointers Operations Dynamic storage management or indirect addressing?
Assignment and dereferencing
Dynamic storage management or indirect addressing?
Scope/lifetime of pointers and associated dynamic objects?
Problems
Dangling references, lost objects
Storage management
Reference counts, garbage collection
Java allows only references
Implicit deallocation