The public type singleTon must be defined in its own file

This statement is not entirely true. While it is true that it is a common practice to define a singleton class in its own file, it is not a requirement or a rule that must be followed.

A singleton class is a class that can have only one instance, and it is often used in scenarios where you want to ensure that there is only one instance of a class in the entire application.

The implementation of a singleton class can vary depending on the programming language and the specific requirements of the application. In some cases, it may make sense to define the singleton class in the same file as other related classes or in a file that contains utility classes.

However, it is important to note that defining a singleton class in its own file can help to improve the clarity and organization of the code. It can also make it easier to maintain and modify the singleton class in the future.