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* @license Apache-2.0
*
* Copyright (c) 2025 The Stdlib Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/* eslint-disable no-invalid-this */
'use strict';
// MODULES //
var setNonEnumerableReadOnly = require( '@stdlib/utils/define-nonenumerable-read-only-property' );
var setNonEnumerable = require( '@stdlib/utils/define-nonenumerable-property' );
var setReadWriteAccessor = require( '@stdlib/utils/define-read-write-accessor' );
var resolveGetter = require( '@stdlib/array/base/resolve-getter' );
var accessors = require( '@stdlib/array/base/accessors' );
var copy = require( '@stdlib/array/base/copy' );
// MAIN //
/**
* Converts each nested array to a composite view.
*
* ## Notes
*
* - The function assumes that all nested arrays have the same length.
* - The number of provided array labels should equal the length of each nested array.
* - Each view in the returned array shares the same memory as the corresponding elements in the input arrays. Accordingly, mutation of either a nested array or a view will mutate the other.
*
* @param {Collection<Collection>} arr - input array
* @param {ArrayLikeObject<string>} fields - list of field names
* @returns {Array<Object>} output array
*
* @example
* var x = [ [ 1, 2 ], [ 3, 4 ] ];
* var fields = [ 'x', 'y' ];
*
* var out = nested2views( x, fields );
* // returns [ <Object>, <Object> ]
*
* var v0 = out[ 0 ].toJSON();
* // returns { 'x': 1, 'y': 2 }
*
* var v1 = out[ 1 ].toJSON();
* // returns { 'x': 3, 'y': 4 }
*
* // Mutate the first nested array:
* x[ 0 ][ 0 ] = 5;
*
* v0 = out[ 0 ].toJSON();
* // returns { 'x': 5, 'y': 2 }
*
* // Set a view property:
* out[ 1 ].y = 'beep';
*
* v1 = out[ 1 ].toJSON();
* // returns { 'x': 3, 'y': 'beep' }
*
* var y = x.slice();
* // returns [ [ 5, 2 ], [ 3, 'beep' ] ]
*/
function nested2views( arr, fields ) {
var oget;
var keys;
var out;
var M;
var N;
var i;
M = arr.length;
if ( M < 1 ) {
return [];
}
oget = resolveGetter( arr );
N = oget( arr, 0 ).length;
if ( N < 1 ) {
return [];
}
// Create a copy of provided fields to prevent external mutation:
keys = copy( fields );
// eslint-disable-next-line stdlib/jsdoc-typedef-typos
/**
* Constructor for creating a composite view.
*
* @private
* @constructor
* @param {Collection} arr - nested array
* @param {NonNegativeInteger} i - element index
* @returns {Datum} datum instance
*/
function Datum( arr, i ) {
var acc = accessors( arr ).accessors;
setNonEnumerable( this, '_arr', arr );
setNonEnumerable( this, '_get', acc[ 0 ] );
setNonEnumerable( this, '_set', acc[ 1 ] );
setNonEnumerableReadOnly( this, '_i', i );
return this;
}
// Define accessors for each field...
for ( i = 0; i < N; i++ ) {
setReadWriteAccessor( Datum.prototype, keys[ i ], getValue( i ), setValue( i ) ); // eslint-disable-line max-len
}
// Define a method for ensuring that cached references are up-to-date:
setNonEnumerableReadOnly( Datum.prototype, '_updateCache', updateCache );
// Ensure that the returned array correctly serializes to JSON:
setNonEnumerableReadOnly( Datum.prototype, 'toJSON', toJSON );
// Create a list of composite views...
out = [];
for ( i = 0; i < M; i++ ) {
out.push( new Datum( oget( arr, i ), i ) );
}
return out;
/**
* Updates cached references, if necessary.
*
* @private
*/
function updateCache() {
var acc;
var ref;
ref = oget( arr, this._i );
if ( ref !== this._arr ) {
acc = accessors( ref ).accessors;
this._arr = ref;
this._get = acc[ 0 ];
this._set = acc[ 1 ];
}
}
/**
* Returns an accessor for returning the value associated with a field.
*
* @private
* @param {NonNegativeInteger} idx - field index
* @returns {Function} accessor
*/
function getValue( idx ) {
return get;
/**
* Returns the value associated with a field.
*
* @private
* @returns {*} result
*/
function get() {
this._updateCache();
return this._get( this._arr, idx );
}
}
/**
* Returns an accessor for setting the value associated with a field.
*
* @private
* @param {NonNegativeInteger} idx - field index
* @returns {Function} accessor
*/
function setValue( idx ) {
return set;
/**
* Sets the value associated with a field.
*
* @private
* @param {*} value - value to set
*/
function set( value ) {
this._updateCache();
this._set( this._arr, idx, value );
}
}
/**
* Serializes a datum to JSON.
*
* @private
* @returns {Object} JSON object
*/
function toJSON() {
var out;
var k;
var i;
out = {};
for ( i = 0; i < N; i++ ) {
k = keys[ i ];
out[ k ] = this[ k ];
}
return out;
}
}
// EXPORTS //
module.exports = nested2views;
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