Binding and Object Lifetime in Programming Languages, Study notes of Programming Languages

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1

Programming Languages

Tevfik Koşar

Lecture - VII February 7th, 2006

2

Roadmap

• Names
• Scopes
• Binding
  • Binding Times
  • Static vs Dynamic Binding
  • Object Lifetime & Storage Management

3

Name, Scope, and Binding

• A name is exactly what you think it is
  • Most names are identifiers
    • Constants, variables, functions
  • symbols (like '+') can also be names
• A binding is an association between two things,

such as a name and the thing it names

• The scope of a binding is the part of the

program (textually)in which the binding is

active

4

Binding Time

• Binding Time is the point at which a binding is

created or, more generally, the point at which

any implementation decision is made

• language design time
  • program structure, control flow, possible types
• language implementation time
  • Coupling of I/O to OS
  • arithmetic overflow
  • Maximum sizes of stack and heap
  • Precision of the (number of bits) of fundamental types

7

Static vs Dynamic Binding

• The terms STATIC and DYNAMIC are generally

used to refer to things bound before run time

and at run time, respectively

• “static”
  binding before run time
• "dynamic“
  binding at run time

8

Binding

• In general, early binding times are associated

with greater efficiency

• Later binding times are associated with greater

flexibility

• Compiled languages tend to have early binding

times

• Interpreted languages tend to have later

binding times

9

Object Lifetime

• Key events
  • creation of objects
  • creation of bindings
  • references to variables (which use bindings)
  • (temporary) deactivation of bindings
  • reactivation of bindings
  • destruction of bindings
  • destruction of objects

10

Object Lifetime

• The period of time from creation to destruction is called the LIFETIME of a binding - If object outlives binding it's garbage - If binding outlives object it's a dangling reference
• The textual region of the program in which the binding is active is its scope
• In addition to talking about the scope of a binding, we sometimes use the word scope as a noun all by itself, without an indirect object