# fold<T> method

T fold <T>(T initialValue, T combine(T previousValue, E element))

Reduces a collection to a single value by iteratively combining each element of the collection with an existing value

Uses `initialValue` as the initial value, then iterates through the elements and updates the value with each element using the `combine` function, as if by:

    var value = initialValue;
    for (E element in this) {
      value = combine(value, element);
    }
    return value;

Example of calculating the sum of an iterable:

    iterable.fold(0, (prev, element) => prev + element);

## Implementation

    T fold<T>(T initialValue, T combine(T previousValue, E element)) {
      var value = initialValue;
      int length = this.length;
      for (int i = 0; i < length; i++) {
        value = combine(value, this[i]);
        if (length != this.length) {
          throw new ConcurrentModificationError(this);
        }
      }
      return value;
    }