findIndex<T> function

int findIndex<T>(List<T> array, [ Predicate<T>? predicate, int fromIndex = 0 ])

Returns the index of the first element in the list that satisfies the provided predicate function. If no such element is found, returns -1.

The predicate function is an optional parameter that takes three arguments: the current element, the index of the current element, and the entire list. If predicate is not provided, the default predicate will be used which checks if the element is not null.

The fromIndex parameter specifies the index to start the search from. It defaults to 0.

Example:

List<int> numbers = [1, 2, 3, 4, 5];
int index = findIndex(numbers, (value, index, array) => value == 3);
print(index); // Output: 2

List<String> words = ['apple', 'banana', 'cherry'];
int index = findIndex(words, (value, index, array) => value.startsWith('b'));
print(index); // Output: 1

List<int?> mixed = [null, 1, 2, null];
int index = findIndex(mixed);
print(index); // Output: 1

• Parameter array: The list to search in.
• Parameter predicate: The function to test each element. Default is a function that checks for non-null values.
• Parameter fromIndex: The index to start the search from. Default is 0.
• Returns: The index of the first element that satisfies the predicate, or -1 if no element satisfies the predicate.

Implementation

int findIndex<T>(List<T> array, [Predicate<T>? predicate, int fromIndex = 0]) {
  predicate ??= (value, index, array) => value != null;

  for (var i = fromIndex; i < array.length; i++) {
    if (predicate(array[i], i, array)) {
      return i;
    }
  }

  return -1;
}