ExtensionAccesses.swift

struct Test {
    func a() {
        b()
        c() // can access if in same file (fileprivate)
        d() // same (private)
        e() // same (private extension)
        f() // same (private extension and private method)
    }
}

extension Test {
    func b() {
        f() // can access even if it's extension is also private
    }

    fileprivate func c() {}

    private func d() {}
}

private extension Test {
    func e() {
        d() // can access while it's still private
    }

    private func f() {}

    // gives a warning when defining fileprivate func within private extension
    //fileprivate func g() {}
}

// In another file
let test = Test()
test.a()
test.b()
//test.c() // can't access
//test.d() // can't access
test.e()
//test.f() // can't access