<divclass="platform-hinted "data-platform-hinted="data-platform-hinted"><divclass="content sourceset-dependent-content"data-active=""data-togglable=":kmath-core:dokkaHtmlPartial/commonMain"><divclass="symbol monospace"><spanclass="token keyword">abstract </span><spanclass="token keyword"></span><spanclass="token keyword">val </span><ahref="indexer.html">indexer</a><spanclass="token operator">: </span><ahref="../-symbol-indexer/index.html">SymbolIndexer</a><spanclass="clearfix"><spanclass="floating-right">(<ahref="https://github.com/SciProgCentre/kmath/tree/master/kmath-core/src/commonMain/kotlin/space/kscience/kmath/expressions/Expression.kt#L39">source</a>)</span></span></div><pclass="paragraph">The indexer of this expression's arguments that should be used to build array for <ahref="invoke.html">invoke</a>.</p><pclass="paragraph">Implementations must fulfil the following requirement: for any argument symbol <codeclass="lang-kotlin">x</code> and its value <codeclass="lang-kotlin">y</code>, <codeclass="lang-kotlin">indexer.indexOf(x) == arguments.indexOf(y)</code> if <codeclass="lang-kotlin">arguments</code> is the array passed to <ahref="invoke.html">invoke</a>.</p></div></div>