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consarray.mjs
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92 lines (86 loc) · 3.16 KB
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// Copyright 2009 the V8 project authors. All rights reserved.
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following
// disclaimer in the documentation and/or other materials provided
// with the distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived
// from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
/**
* Constructs a ConsArray object. It is used mainly for tree traversal.
* In this use case we have lots of arrays that we need to iterate
* sequentally. The internal Array implementation is horribly slow
* when concatenating on large (10K items) arrays due to memory copying.
* That's why we avoid copying memory and insead build a linked list
* of arrays to iterate through.
*
* @constructor
*/
export class ConsArray {
constructor() {
this.tail_ = new ConsArrayCell(null, null);
this.currCell_ = this.tail_;
this.currCellPos_ = 0;
}
/**
* Concatenates another array for iterating. Empty arrays are ignored.
* This operation can be safely performed during ongoing ConsArray
* iteration.
*
* @param {Array} arr Array to concatenate.
*/
concat(arr) {
if (arr.length > 0) {
this.tail_.data = arr;
this.tail_ = this.tail_.next = new ConsArrayCell(null, null);
}
}
/**
* Whether the end of iteration is reached.
*/
atEnd() {
return this.currCell_ === null ||
this.currCell_.data === null ||
this.currCellPos_ >= this.currCell_.data.length;
}
/**
* Returns the current item, moves to the next one.
*/
next() {
const result = this.currCell_.data[this.currCellPos_++];
if (this.currCellPos_ >= this.currCell_.data.length) {
this.currCell_ = this.currCell_.next;
this.currCellPos_ = 0;
}
return result;
}
}
/**
* A cell object used for constructing a list in ConsArray.
*
* @constructor
*/
class ConsArrayCell {
constructor(data, next) {
this.data = data;
this.next = next;
}
}