Lesson 10.3: Semantic Issues of Variables: Scoping

Scope

range of statements in which the variable is visible

Scope

a variable is visible in a statement if it can be referenced in that statement

Block

section of code that may have their won stack-dynamic variables, and usually defines a scope

Local Variables

variables that are declared on the current block

Global Variable

can be accessed at any given point at any given time within the entirety of the program

Nonlocal Variable

variables that are visible to a block but is not declared there

Static and Dynamic Scoping

two types of scoping

Static scoping

scope of a variable is statically determined

Static scoping

allows the support for nested subprograms, program blocks and class definitions

Static parent

enclosing block where the current block is written

Static ancestor

all enclosing blocks of the current block

Enclosing block

every time a variable is used, the _ _ is checked

Static ancestor

if the variable is not found, the _ _ are searched

Dynamic Scoping

variable scope is determined by the sequence of calls to the subprograms

Dynamic Parent

the subprogram that called the current subprogram

Dynamic Ancestor

all subprogram calls that led to the current subprogram

Same Variable

variable name may not refer to the _ _, disadvantage of dynamic scoping (1)

Statistically

some attributes cannot be determined _, disadvantage of dynamic scoping (2)

Harder to read

source code may be _ _ _ , disadvantage of dynamic scoping (3)

Nonlocal variables

access to _ _ are slower, disadvantage of dynamic scoping (4)

Not Equal

Lifetime and Scope are _ _

Referencing Environment

collection of all variables visible in a statement

Only Once

named constants, variables bound to a value _ _

Initialization

binding of a value to a variable upon storage binding