Function createCursor

packages/react-reconciler/src/ReactFiberStack.js:24–28

(defaultValue: T)

let index = -1;

function createCursor<T>(defaultValue: T): StackCursor<T> {
  return {
    current: defaultValue,
  };
}

function pop<T>(cursor: StackCursor<T>, fiber: Fiber): void {
  if (index < 0) {