Swift Tutorial - Tutorialspoint

To restrict access to code blocks, modules and abstraction is done through access control.
Classes, structures and enumerations can be accessed according to their properties,
methods, initializers and subscripts by access control mechanisms. Constants, variables
and functions in a protocol are restricted and allowed access as global and local through
access control. Access control applied to properties, types and functions can be referred
as 'entities'.

Access control model is based on modules and source files.

Module is defined as a single unit of code distribution and can be imported using the
keyword 'import'. A source file is defined as a single source code file with in a module to
access multiple types and functions.

Three different access levels are provided by Swift language. They are Public, Internal and
Private access.

Access

Levels Definition^

Public

Enables entities to be processed with in any source file from their defining

module, a source file from another module that imports the defining

module.

Internal Enables entities to be used within any source file from^ their defining

module, but not in any source file outside of that module.

Private

Restricts the use of an entity to its own defining source file. Private access

plays role to hide the implementation details of a specific code functionality.

Syntax

public class SomePublicClass {}

internal class SomeInternalClass {}

private class SomePrivateClass {}

public var somePublicVariable = 0

internal let someInternalConstant = 0

private func somePrivateFunction() {}

Access Control for Function types

Some functions may have arguments declared inside the function without any return
values. The following program declares a and b as arguments to the sum() function. Inside
the function itself the values for arguments a and b are passed by invoking the function

33. SWIFT – ACCESS CONTROL