What restrictions exist when overriding functions in programming?

When overriding functions (methods) in programming, the following restrictions apply:

• The method must have the same signature (name, parameters) and return type (or a compatible one).
• The visibility of the method cannot be made more restrictive (for example, from public to private).
• In some languages, static methods cannot be overridden.
• Exceptions that the method can throw must be compatible with the base method (for example, not expanding the list of checked exceptions).
• In Swift, for example, the method must be declared with the override keyword.

These restrictions ensure correct polymorphism operation and prevent runtime errors.