Method _getExpansionKey

src/cdk/tree/tree.ts:953–962

(dataNode: T)

  }

  private _getExpansionKey(dataNode: T): K {
    // In the case that a key accessor function was not provided by the
    // tree user, we'll default to using the node object itself as the key.
    //
    // This cast is safe since:
    // - if an expansionKey is provided, TS will infer the type of K to be
    //   the return type.
    // - if it's not, then K will be defaulted to T.
    return this.expansionKey?.(dataNode) ?? (dataNode as unknown as K);
  }

  private _getAriaSet(node: T) {
    const key = this._getExpansionKey(node);