educes a collection to a single value by iteratively combining each
element of the collection with an existing value</p>
<p>Uses <code>initialValue</code> as the initial value,
then iterates through the elements and updates the value with
each element using the <code>combine</code> function, as if by:</p>
<pre class="language-dart"><code>var value = initialValue;
for (E element in this) {
  value = combine(value, element);
}
return value;
</code></pre>
<p>Example of calculating the sum of an iterable:</p>
<