net.sf.saxon.value.package-info Maven / Gradle / Ivy
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// Copyright (c) 2018-2023 Saxonica Limited
// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
// If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
// This Source Code Form is "Incompatible With Secondary Licenses", as defined by the Mozilla Public License, v. 2.0.
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/**
* This package provides classes representing XPath values (that is, the results of
* an expression). There are different classes for different types of value.
* The principal class is:
* Value:
* This represents the result of evaluating an expression. But a Value is also an expression in its
* own right, reflecting the fact that literal values can be used syntactically wherever expressions
* can be used. AtomicValue is a subclass of Value
* that represents an atomic value: this in turn has subclasses for the different built-in data types:
* StringValue, NumericValue, BooleanValue, DateValue, and so on.
* There are two classes used to represent integer values: IntegerValue for integers that
* fit comfortably in 64 bits, and BigIntegerValue for anything longer. Built-in subtypes
* of xs:integer, such as xs:int and xs:short, are always represented using
* an IntegerValue, except for xs:unsignedLong, which uses a BigIntegerValue.
*
* In general a value is a sequence. A sequence that is instantiated in memory is represented by a
* SequenceExtent object. The code tries to pipeline execution so that a SequenceExtent
* is created as rarely as possible.
* When an expression is evaluated lazily, the result is a Closure. A Closure contains the original
* expression, and a copy of the run-time context at the time evaluation was requested: that is, all the local
* variables
* and other information that it depends on, such as the context item. There are two kinds of Closure, and the system
* decides at compile time which to use. An ordinary Closure re-evaluates the expression every time the value is
* referenced;
* this is used only when the compiler decides that the value is likely to be referenced only once. A MemoClosure
* remembers
* the value the first time it is needed, so that subsequent references do not cause repeated evaluation of the
* expression.
*/
package net.sf.saxon.value;