# length property

The number of elements in this.

Counting all elements may involve iterating through all elements and can
therefore be slow.
Some iterables have a more efficient way to find the number of elements.
These *must* override the default implementation of `length`

.

## Implementation

```
int get length {
assert(this is! EfficientLengthIterable);
int count = 0;
Iterator<Object?> it = iterator;
while (it.moveNext()) {
count++;
}
return count;
}
```