List<E> class Null safety

An indexable collection of objects with a length.

Subclasses of this class implement different kinds of lists. The most common kinds of lists are:

• Fixed-length list. An error occurs when attempting to use operations that can change the length of the list.

• Growable list. Full implementation of the API defined in this class.

The default growable list, as created by [], keeps an internal buffer, and grows that buffer when necessary. This guarantees that a sequence of add operations will each execute in amortized constant time. Setting the length directly may take time proportional to the new length, and may change the internal capacity so that a following add operation will need to immediately increase the buffer capacity. Other list implementations may have different performance behavior.

The following code illustrates that some List implementations support only a subset of the API.

var fixedLengthList = List<int>.filled(5, 0);
fixedLengthList.length = 0;  // Error
fixedLengthList.add(499);    // Error
fixedLengthList[0] = 87;
var growableList = [1, 2];
growableList.length = 0;
growableList.add(499);
growableList[0] = 87;

Lists are Iterable. Iteration occurs over values in index order. Changing the values does not affect iteration, but changing the valid indices—that is, changing the list's length—between iteration steps causes a ConcurrentModificationError. This means that only growable lists can throw ConcurrentModificationError. If the length changes temporarily and is restored before continuing the iteration, the iterator might not detect it.

It is generally not allowed to modify the list's length (adding or removing elements) while an operation on the list is being performed, for example during a call to forEach or sort. Changing the list's length while it is being iterated, either by iterating it directly or through iterating an Iterable that is backed by the list, will break the iteration.