sumE<TResult extends num> method

TResult sumE <TResult extends num>([Selector<T, TResult> selector ])

Calculates the sum of the elements in an enumerable, optionally using selector to obtain the value to be summed.

Iterates over the entire enumerable, passing each element to the selector function and adding its return value to a running total. Once iteration is complete, the total is returned.

The type of the returned total is dependent on the value returned by the selector function. If all values are int, the return value of sumE will be int. If all values are double, the return value of sumE will be double. If all values are num or there is a combination of int and double, the return value of sumE will be num.

When the type of the enumerable is a numeric primitive (e.g. int, double, or num), the selector function can be omitted. If so, the elements themselves are added to the running total.

If the type of the enumerable is not a numeric primitive, the selector function must be provided. Otherwise, an ArgumentError is thrown.

Implementation

TResult sumE<TResult extends num>([Selector<T, TResult> selector]) {
  IncompatibleTypeError.checkValidTypeOrParam(
      T, SumReducers.director.keys, selector);

  if (selector == null) {
    return SumReducers.director[T](this);
  }

  num sum;

  if (TResult == int) {
    sum = 0;
  } else {
    sum = 0.0;
  }

  final _iterator = this.iterator;

  if (!_iterator.moveNext()) {
    throw EnumerableError.isEmpty();
  }

  do {
    sum += selector(_iterator.current);
  } while (_iterator.moveNext());

  return sum;
}