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Complex Data Types in Programming

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  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 • 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 • 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 • Faster than array subscripts • Elliptical references (COBOL, PL/I) • Operations • Move corresponding

  13. Unions

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

  15. Sets • Pascal, Java

  16. Pointers

  17. Pointers • Operations • 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

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