Types and Related Issues Bindings

Bindings Are factors that characterize objects name location value type scope lifetime

Bindings (continued) Can be static or dynamic Can occur at many different times: language design operator symbols to operations language implementation range of values for integers compile variable to type link call to library subprogram load static variables to memory cells run value to variable

Names

Names Format Aliasing length character set case reserved word or keyword for meaningful names in the language? Aliasing

Location

Location Static Stack dynamic Explicit heap dynamic Implicit heap dynamic rare, used in APL and Algol-68

Type

Type Primitive or complex Usually bound statically Coercion or casting but can be dynamic in LISP, APL, SNOBOL Coercion or casting Strong typing language “always detects type errors” Name compatibility or structure compatibility name: same declaration or same type name easier to implement but restrictive structure: same internal structure may not be strict enough

Type (continued) Most languages use a combination of equivalence methods Pascal: usually structure, but in some cases name is used (formal parameters) C: structure, except for records C++: name Ada: restricted form of name derived types allow types with the same structure to be different type celcius is new real; type fahrenheit is new real; subtype allows types to be compatible even with different names subtype digit is INTEGER range 0..9;

Scope

Scope Range of statements in a program when a name can be referenced (is visible) Controlled by subprograms, compound statements Static most languages Dynamic APL, SNOBOL, some LISPs means no compile-time type checking of non-local objects

Lifetime

Period when data object is allocated memory Can be different than scope hole in scope static variables invoking external subprogram