How to estimate the time complexity of reading an element by index in an array?

In an array (for example, in a Dart list or an array in any language), the operation of reading an element by index usually has a time complexity of O(1) — constant time.

This is because arrays are implemented as contiguous blocks of memory, and access to an element by index reduces to calculating the address of the element (starting address + index * size of element) and reading the value at that address.

Example in Dart:

List<int> numbers = [10, 20, 30, 40];
int value = numbers[2]; // Fast access to the element with O(1) complexity

Thus, reading by index in an array is a very efficient operation.