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/*
* Copyright (c) 2012-2017 The ANTLR Project. All rights reserved.
* Use of this file is governed by the BSD 3-clause license that
* can be found in the LICENSE.txt file in the project root.
*/
package org.antlr.v4.runtime;
/**
* A simple stream of symbols whose values are represented as integers. This
* interface provides marked ranges with support for a minimum level
* of buffering necessary to implement arbitrary lookahead during prediction.
* For more information on marked ranges, see {@link #mark}.
*
* Initializing Methods: Some methods in this interface have
* unspecified behavior if no call to an initializing method has occurred after
* the stream was constructed. The following is a list of initializing methods:
*
*
* - {@link #LA}
* - {@link #consume}
* - {@link #size}
*
*/
public interface IntStream {
/**
* The value returned by {@link #LA LA()} when the end of the stream is
* reached.
*/
public static final int EOF = -1;
/**
* The value returned by {@link #getSourceName} when the actual name of the
* underlying source is not known.
*/
public static final String UNKNOWN_SOURCE_NAME = "";
/**
* Consumes the current symbol in the stream. This method has the following
* effects:
*
*
* - Forward movement: The value of {@link #index index()}
* before calling this method is less than the value of {@code index()}
* after calling this method.
* - Ordered lookahead: The value of {@code LA(1)} before
* calling this method becomes the value of {@code LA(-1)} after calling
* this method.
*
*
* Note that calling this method does not guarantee that {@code index()} is
* incremented by exactly 1, as that would preclude the ability to implement
* filtering streams (e.g. {@link CommonTokenStream} which distinguishes
* between "on-channel" and "off-channel" tokens).
*
* @throws IllegalStateException if an attempt is made to consume the
* end of the stream (i.e. if {@code LA(1)==}{@link #EOF EOF} before calling
* {@code consume}).
*/
void consume();
/**
* Gets the value of the symbol at offset {@code i} from the current
* position. When {@code i==1}, this method returns the value of the current
* symbol in the stream (which is the next symbol to be consumed). When
* {@code i==-1}, this method returns the value of the previously read
* symbol in the stream. It is not valid to call this method with
* {@code i==0}, but the specific behavior is unspecified because this
* method is frequently called from performance-critical code.
*
* This method is guaranteed to succeed if any of the following are true:
*
*
* - {@code i>0}
* - {@code i==-1} and {@link #index index()} returns a value greater
* than the value of {@code index()} after the stream was constructed
* and {@code LA(1)} was called in that order. Specifying the current
* {@code index()} relative to the index after the stream was created
* allows for filtering implementations that do not return every symbol
* from the underlying source. Specifying the call to {@code LA(1)}
* allows for lazily initialized streams.
* - {@code LA(i)} refers to a symbol consumed within a marked region
* that has not yet been released.
*
*
* If {@code i} represents a position at or beyond the end of the stream,
* this method returns {@link #EOF}.
*
* The return value is unspecified if {@code i<0} and fewer than {@code -i}
* calls to {@link #consume consume()} have occurred from the beginning of
* the stream before calling this method.
*
* @throws UnsupportedOperationException if the stream does not support
* retrieving the value of the specified symbol
*/
int LA(int i);
/**
* A mark provides a guarantee that {@link #seek seek()} operations will be
* valid over a "marked range" extending from the index where {@code mark()}
* was called to the current {@link #index index()}. This allows the use of
* streaming input sources by specifying the minimum buffering requirements
* to support arbitrary lookahead during prediction.
*
* The returned mark is an opaque handle (type {@code int}) which is passed
* to {@link #release release()} when the guarantees provided by the marked
* range are no longer necessary. When calls to
* {@code mark()}/{@code release()} are nested, the marks must be released
* in reverse order of which they were obtained. Since marked regions are
* used during performance-critical sections of prediction, the specific
* behavior of invalid usage is unspecified (i.e. a mark is not released, or
* a mark is released twice, or marks are not released in reverse order from
* which they were created).
*
* The behavior of this method is unspecified if no call to an
* {@link IntStream initializing method} has occurred after this stream was
* constructed.
*
* This method does not change the current position in the input stream.
*
* The following example shows the use of {@link #mark mark()},
* {@link #release release(mark)}, {@link #index index()}, and
* {@link #seek seek(index)} as part of an operation to safely work within a
* marked region, then restore the stream position to its original value and
* release the mark.
*
* IntStream stream = ...;
* int index = -1;
* int mark = stream.mark();
* try {
* index = stream.index();
* // perform work here...
* } finally {
* if (index != -1) {
* stream.seek(index);
* }
* stream.release(mark);
* }
*
*
* @return An opaque marker which should be passed to
* {@link #release release()} when the marked range is no longer required.
*/
int mark();
/**
* This method releases a marked range created by a call to
* {@link #mark mark()}. Calls to {@code release()} must appear in the
* reverse order of the corresponding calls to {@code mark()}. If a mark is
* released twice, or if marks are not released in reverse order of the
* corresponding calls to {@code mark()}, the behavior is unspecified.
*
* For more information and an example, see {@link #mark}.
*
* @param marker A marker returned by a call to {@code mark()}.
* @see #mark
*/
void release(int marker);
/**
* Return the index into the stream of the input symbol referred to by
* {@code LA(1)}.
*
* The behavior of this method is unspecified if no call to an
* {@link IntStream initializing method} has occurred after this stream was
* constructed.
*/
int index();
/**
* Set the input cursor to the position indicated by {@code index}. If the
* specified index lies past the end of the stream, the operation behaves as
* though {@code index} was the index of the EOF symbol. After this method
* returns without throwing an exception, then at least one of the following
* will be true.
*
*
* - {@link #index index()} will return the index of the first symbol
* appearing at or after the specified {@code index}. Specifically,
* implementations which filter their sources should automatically
* adjust {@code index} forward the minimum amount required for the
* operation to target a non-ignored symbol.
* - {@code LA(1)} returns {@link #EOF}
*
*
* This operation is guaranteed to not throw an exception if {@code index}
* lies within a marked region. For more information on marked regions, see
* {@link #mark}. The behavior of this method is unspecified if no call to
* an {@link IntStream initializing method} has occurred after this stream
* was constructed.
*
* @param index The absolute index to seek to.
*
* @throws IllegalArgumentException if {@code index} is less than 0
* @throws UnsupportedOperationException if the stream does not support
* seeking to the specified index
*/
void seek(int index);
/**
* Returns the total number of symbols in the stream, including a single EOF
* symbol.
*
* @throws UnsupportedOperationException if the size of the stream is
* unknown.
*/
int size();
/**
* Gets the name of the underlying symbol source. This method returns a
* non-null, non-empty string. If such a name is not known, this method
* returns {@link #UNKNOWN_SOURCE_NAME}.
*/
public String getSourceName();
}