Why Does 'abcd'.StartsWith('') Return True?

Why "abcd".StartsWith("") Returns True

The question arises: why does "abcd".StartsWith("") evaluate to true?

The answer lies in the concept of an empty string. An empty string, as its name suggests, is a string with zero characters. It represents the absence of any characters.

In the context of the StartsWith method, an empty string is considered a legitimate "substring" of any other string. This is because, logically, the empty string occurs between every pair of characters in any string.

Consider the following definition of "starts with":

• A string x starts with y if the first y.Length characters of x match those of y.

Using this definition, we can see that "abcd".StartsWith("") is indeed true. The empty string has zero characters, so its length is also zero. The first zero characters of "abcd" are also a match for the first zero characters of the empty string. Therefore, "abcd" starts with the empty string.

Another equivalent definition of "starts with" is:

• A string x starts with y if x.Substring(0, y.Length).Equals(y)

This definition gives us another way to visualize the result of "abcd".StartsWith(""). Calling x.Substring(0, y.Length) extracts a substring from x starting at index 0 and ending just before index y.Length. In this case, y.Length is zero, so the substring extracted from "abcd" is an empty string. Since an empty string is equal to the empty string y, the StartsWith method returns true.

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