Accumulator<T, U> typedef

A function used to accumulate values in reduction operations.

Takes an accumulator of type U and a current value of type T, returning a new accumulator.

{@tool snippet}

final Accumulator<int, int> sum = (acc, value) => acc + value;
final total = [1, 2, 3, 4].reduce((a, b) => sum(a, b));
print(total); // 10

{@end-tool}