org.basex.query.util

Class Var

java.lang.Object

org.basex.data.ExprInfo

org.basex.query.expr.Expr

org.basex.query.expr.ParseExpr

org.basex.query.util.Var

public final class Var
extends ParseExpr

Variable expression.

Author:

BaseX Team 2005-12, BSD License, Christian Gruen

Nested Class Summary

Nested classes/interfaces inherited from class org.basex.query.expr.Expr

Expr.Use

Field Summary

Fields

Modifier and Type	Field and Description
Ann	ann Annotations.
boolean	declared Declaration flag.
boolean	global Global flag.
QNm	name Variable name.
SeqType	ret Expected return type.

Fields inherited from class org.basex.query.expr.ParseExpr

input, size, type

Method Summary

Methods

Modifier and Type	Method and Description
Var	bind(Expr e, QueryContext ctx) Binds the specified expression to the variable.
Var	bind(Value v, QueryContext ctx) Binds the specified value to the variable.
void	checkUp() Checks if the variable contains no updating expression.
Var	comp(QueryContext ctx) Compiles and optimizes the expression, assigns data types and cardinalities.
Var	copy() Returns a copy of the variable.
int	count(Var v) Counts how often the specified variable is used by an expression.
static Var	create(QueryContext ctx, InputInfo ii, QNm n, Ann a) Creates a new variable.
static Var	create(QueryContext ctx, InputInfo ii, QNm n, SeqType t, Ann a) Creates a new variable.
static Var	create(QueryContext ctx, InputInfo ii, QNm n, Value v, Ann a) Creates a new variable.
Expr	expr() Returns the bound expression.
boolean	is(Var v) Checks whether the given variable is identical to this one, i.e.
Item	item(QueryContext ctx, InputInfo ii) Evaluates the expression and returns the resulting item or a null reference, if the expression yields an empty sequence.
Iter	iter(QueryContext ctx) Evaluates the expression and returns an iterator on the resulting items.
void	plan(Serializer ser) Serializes the expression tree.
boolean	removable(Var v) Checks if the specified variable is replaceable by a context item.
Var	remove(Var v) Substitutes all VarRef expressions for the given variable by a Context reference.
void	reset(SeqType t, QueryContext ctx) Sets the specified variable type.
boolean	sameAs(Expr cmp) Compares the current and specified expression for equality.
java.lang.String	toString()
SeqType	type() Returns the sequence type of the evaluated value.
boolean	uses(Expr.Use u) Indicates if an expression uses the specified type or operation.
Value	value(QueryContext ctx) Evaluates the expression and returns the resulting value.

Methods inherited from class org.basex.query.expr.ParseExpr

checkBln, checkColl, checkCreate, checkCtx, checkDbl, checkDBNode, checkEStr, checkEStr, checkIO, checkItem, checkItr, checkItr, checkMap, checkNode, checkNoEmpty, checkStr, checkType, checkUp, checkUp, checkWrite, compBln, ebv, optPre, preEval, size, test

Methods inherited from class org.basex.query.expr.Expr

addText, compEbv, hasFreeVars, indexAccessible, indexEquivalent, isEmpty, isFunction, isItem, isVacuous, isValue, iterable, markTailCalls

Methods inherited from class org.basex.data.ExprInfo

description, info

Methods inherited from class java.lang.Object

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

Field Detail

name

public final QNm name

Variable name.

ann

public final Ann ann

Annotations.

ret

public SeqType ret

Expected return type.

global

public boolean global

Global flag.

declared

public boolean declared

Declaration flag.

Method Detail

create

public static Var create(QueryContext ctx,
         InputInfo ii,
         QNm n,
         SeqType t,
         Ann a)

Creates a new variable.

Parameters:

ctx - query context

ii - input info

n - variable name

t - type

a - annotations

Returns:

variable

create

public static Var create(QueryContext ctx,
         InputInfo ii,
         QNm n,
         Ann a)

Creates a new variable.

Parameters:

ctx - query context

ii - input info

n - variable name

a - annotations

Returns:

variable

create

public static Var create(QueryContext ctx,
         InputInfo ii,
         QNm n,
         Value v,
         Ann a)

Creates a new variable.

Parameters:

ctx - query context

ii - input info

n - variable name

v - variable to be bound

a - annotations

Returns:

variable

checkUp

public void checkUp()
             throws QueryException

Checks if the variable contains no updating expression.

Throws:

QueryException - query exception

comp

public Var comp(QueryContext ctx)
         throws QueryException

Description copied from class: Expr

Compiles and optimizes the expression, assigns data types and cardinalities.

Specified by:

comp in class Expr

Parameters:

ctx - query context

Returns:

optimized expression

Throws:

QueryException - query exception

reset

public void reset(SeqType t,
         QueryContext ctx)
           throws QueryException

Sets the specified variable type.

Parameters:

t - type

ctx - query context

Throws:

QueryException - query exception

bind

public Var bind(Expr e,
       QueryContext ctx)
         throws QueryException

Binds the specified expression to the variable.

Parameters:

e - expression to be set

ctx - query context

Returns:

self reference

Throws:

QueryException - query exception

expr

public Expr expr()

Returns the bound expression.

Returns:

expression

bind

public Var bind(Value v,
       QueryContext ctx)
         throws QueryException

Binds the specified value to the variable.

Parameters:

v - value to be set

ctx - query context

Returns:

self reference

Throws:

QueryException - query exception

item

public Item item(QueryContext ctx,
        InputInfo ii)
          throws QueryException

Description copied from class: Expr

Evaluates the expression and returns the resulting item or a null reference, if the expression yields an empty sequence. If this method is not overwritten, Expr.iter(org.basex.query.QueryContext) must be implemented by an expression, as it may be called by this method.

Overrides:

item in class ParseExpr

Parameters:

ctx - query context

ii - input info

Returns:

iterator

Throws:

QueryException - query exception

iter

public Iter iter(QueryContext ctx)
          throws QueryException

Description copied from class: Expr

Evaluates the expression and returns an iterator on the resulting items. If this method is not overwritten, Expr.item(org.basex.query.QueryContext, org.basex.util.InputInfo) must be implemented by an expression, as it may be called by this method.

Overrides:

iter in class ParseExpr

Parameters:

ctx - query context

Returns:

resulting item

Throws:

QueryException - query exception

value

public Value value(QueryContext ctx)
            throws QueryException

Description copied from class: Expr

Evaluates the expression and returns the resulting value.

Overrides:

value in class ParseExpr

Parameters:

ctx - query context

Returns:

iterator

Throws:

QueryException - query exception

is

public boolean is(Var v)

Checks whether the given variable is identical to this one, i.e. has the same ID.

Parameters:

v - variable to check

Returns:

true, if the IDs are equal, false otherwise

copy

public Var copy()

Returns a copy of the variable.

Returns:

copy

uses

public boolean uses(Expr.Use u)

Description copied from class: Expr

Indicates if an expression uses the specified type or operation. This method is called by numerous Expr.comp(org.basex.query.QueryContext) methods to test the properties of sub-expressions. It will return true as soon as at least one test is successful.

Specified by:

uses in class Expr

Parameters:

u - type/operation to be found

Returns:

result of check

count

public int count(Var v)

Description copied from class: Expr

Counts how often the specified variable is used by an expression. This method is called by:

• GFLWOR.comp(org.basex.query.QueryContext) to rewrite where clauses as predicates and remove statically bound or unused clauses
• GFLWOR.compHoist(org.basex.query.QueryContext) to hoist independent variables

Specified by:

count in class Expr

Parameters:

v - variable to be checked

Returns:

number of occurrences

removable

public boolean removable(Var v)

Description copied from class: Expr

Checks if the specified variable is replaceable by a context item. The following tests might return false:

• Preds.removable(org.basex.query.util.Var), if one of the variables is used within a predicate.
• MixedPath.removable(org.basex.query.util.Var), if the variable occurs within the path.
• Group.removable(org.basex.query.util.Var), as the group by expression depends on variable references.

This method is called by GFLWOR.comp(org.basex.query.QueryContext) to rewrite where clauses into predicates.

Specified by:

removable in class Expr

Parameters:

v - variable to be replaced

Returns:

result of check

remove

public Var remove(Var v)

Description copied from class: Expr

Substitutes all VarRef expressions for the given variable by a Context reference. This method is called by GFLWOR.comp(org.basex.query.QueryContext) to rewrite where clauses as predicates.

Specified by:

remove in class Expr

Parameters:

v - variable to be replaced

Returns:

new expression

type

public SeqType type()

Description copied from class: Expr

Returns the sequence type of the evaluated value. For simplicity, some types have been summarized. E.g., all numbers are treated as integers.

Overrides:

type in class ParseExpr

Returns:

result of check

sameAs

public boolean sameAs(Expr cmp)

Description copied from class: Expr

Compares the current and specified expression for equality.

Overrides:

sameAs in class Expr

Parameters:

cmp - expression to be compared

Returns:

result of check

plan

public void plan(Serializer ser)
          throws java.io.IOException

Description copied from class: ExprInfo

Serializes the expression tree.

Specified by:

plan in class ExprInfo

Parameters:

ser - serializer

Throws:

java.io.IOException - I/O exception

toString

public java.lang.String toString()

Specified by:

toString in class ExprInfo