dk.brics.string.intermediate.operations
Class AliasTable

java.lang.Object
  dk.brics.string.intermediate.operations.AliasTable

public class AliasTable
extends Object

Represents the aliasing status between a set of variables.

This class is responsible for an efficient representation. To this end, the following semantic assumptions are exploited:

• A variable is always definitely an alias of itself.
• Two variables of incompatible types are definitely not aliases.

Those assumptions affect the behaviour of the setAliasStatus(dk.brics.string.intermediate.Variable, dk.brics.string.intermediate.Variable, dk.brics.string.intermediate.operations.AliasStatus) methods in these ways:

• If a variable is assigned to definitely not be an alias of itself, an exception is thrown.
• If a variable is assigned to maybe be an alias of itself (or assigned to BOTTOM), nothing happens.
• If two variables of incompatible types are assigned to definitely be aliases, an exception is thrown.
• If two variables of incompatible types are assigned to maybe be aliases (or assigned to BOTTOM), nothing happens.

Constructor Summary

AliasTable(Set<Variable> variables, AliasStatus initial)
Creates variable aliasings between the specified variables.

Method Summary

AliasStatus	getAliasStatus(UnorderedPair<Variable> pair) Returns the current aliasing status between two variables.
AliasStatus	getAliasStatus(Variable a, Variable b) Returns the current aliasing status between two variables.
boolean	setAliasStatus(UnorderedPair<Variable> pair, AliasStatus status) Sets the current aliasing status between two variables.
boolean	setAliasStatus(Variable a, Variable b, AliasStatus status) Sets the current aliasing status between two variables.
String	toString() Returns the result of toString on the underlying map.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

AliasTable

public AliasTable(Set<Variable> variables,
                  AliasStatus initial)

Creates variable aliasings between the specified variables. Only variables in the specified set may be used in queries to this object.

Parameters:

variables - the variables to track aliasing between.

initial - the initial aliasing status between all pairs of variables

Method Detail

getAliasStatus

public AliasStatus getAliasStatus(UnorderedPair<Variable> pair)

Returns the current aliasing status between two variables.

Parameters:

pair - a pair of variables from the set passed to AliasTable's constructor.

Returns:

an aliasing status. null is never returned.

getAliasStatus

public AliasStatus getAliasStatus(Variable a,
                                  Variable b)

Returns the current aliasing status between two variables.

Parameters:

a - a variable from the set passed to AliasTable's constructor.

b - a variable from the set passed to AliasTable's constructor.

Returns:

an aliasing status. null is never returned.

setAliasStatus

public boolean setAliasStatus(UnorderedPair<Variable> pair,
                              AliasStatus status)

Sets the current aliasing status between two variables. If the two variables are the same, only DEFINITELY is accepted.

Parameters:

pair - a pair of variables from the set passed to AliasTable's constructor.

Returns:

true if something changed

setAliasStatus

public boolean setAliasStatus(Variable a,
                              Variable b,
                              AliasStatus status)

Sets the current aliasing status between two variables. The order of the arguments is irrelevant.

The semantic assumption listed in AliasTable may override the change.

Returns:

true if something changed

toString

public String toString()

Returns the result of toString on the underlying map. Mostly useful when running the integrated debugger.

Overrides:

toString in class Object