I have a question about internal access control level
Internal is default access control level in Swift
so I think all of internal access control should be removed
Is there a specific case of using internal access control explicitly in Swift?
When or How I use internal access control in Swift?
I found a case internal needs to be added explicitly:
public internal(set) var myInt = 0 Omitting the internal keyword results in a compile error.
This is particular useful in a swift package/pod. The property is exposed publicly, but only inside the package/pod, the value can be changed.
As per documentation:
Default Access Levels All entities in your code (with a few specific exceptions, as described later in this chapter) have a default access level of internal if you don’t specify an explicit access level yourself. As a result, in many cases you don’t need to specify an explicit access level in your code.
Source: https://docs.swift.org/swift-book/LanguageGuide/AccessControl.html
As you mentioned, using the "internal" keyword has no effect other than making it clear that a function should never be made public in the future without careful consideration. At this point using the "internal" keyword is more about documenting and commenting your code.
When use default access level internal, no need to add internal explicitly. This means that SomeInternalClass and someInternalConstant can be written without an explicit access-level modifier, and will still have an access level of internal. However the keyword "internal" is used just for developers understanding.
class SomeInternalClass {} // implicitly internal let someInternalConstant = 0 // implicitly internal 
internalmarks the property available in the module only, it is really important when developing a library or framework – obviously it must not be removed.