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* @license Apache-2.0
*
* Copyright (c) 2026 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.
*/
'use strict';
// MODULES //
var isArray = require( '@stdlib/assert/is-array' );
var isPlainObject = require( '@stdlib/assert/is-plain-object' );
var format = require( '@stdlib/string/format' );
var copy = require( '@stdlib/utils/copy' );
var isSafeToken = require( '@stdlib/utils/json-pointer/base/assert/is-safe-token' );
var resolveToken = require( '@stdlib/utils/json-pointer/base/resolve-token' );
// MAIN //
/**
* Immutably sets a value at a path in a document using structural sharing.
*
* @param {(Object|Array)} document - source document
* @param {Array<string>} tokens - array of reference tokens
* @param {*} value - the value to set
* @throws {Error} tokens must not contain unsafe tokens
* @throws {TypeError} intermediate path segments must not reference non-traversable value
* @returns {(Object|Array)} new document with the value set at the specified path
*
* @example
* var doc = {
* 'a': {
* 'b': {
* 'c': 1
* }
* }
* };
* var out = set( doc, [ 'a', 'b', 'c' ], 99 );
* // returns { 'a': { 'b': { 'c': 99 } } }
*
* var bool = ( doc.a.b === out.a.b );
* // returns false
*
* bool = ( doc === out );
* // returns false
*/
function set( document, tokens, value ) {
var current;
var child;
var root;
var key;
var i;
// Root replacement:
if ( tokens.length === 0 ) {
return value;
}
root = copy( document, 1 );
current = root;
// Walk all tokens except the last, cloning each level:
for ( i = 0; i < tokens.length - 1; i++ ) {
if ( !isSafeToken( tokens[ i ] ) ) {
throw new Error( format( 'invalid argument. Token contains an unsafe value. Value: `%s`.', tokens[ i ] ) );
}
key = resolveToken( current, tokens[ i ] );
if ( !isPlainObject( current[ key ] ) && !isArray( current[ key ] ) ) {
throw new TypeError( format( 'invalid argument. Path references a non-traversable value at token `%s`.', tokens[ i ] ) );
}
child = copy( current[ key ], 1 );
current[ key ] = child;
current = child;
}
// Set the value at the final token:
if ( !isSafeToken( tokens[ tokens.length - 1 ] ) ) {
throw new Error( format( 'invalid argument. Token contains an unsafe value. Value: `%s`.', tokens[ tokens.length - 1 ] ) );
}
key = resolveToken( current, tokens[ tokens.length - 1 ] );
current[ key ] = value;
return root;
}
// EXPORTS //
module.exports = set;
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