How to make the property “read-only” outside calls and “read-write” outside class?

Here is the Swift implementation:

public class SomeClass {
    // Read-Only Outside: Public getter, private setter
    public private(set) var readOnlyOutside: Int
    // Read-Write Outside: Public getter and setter
    public var readWriteOutside: Int
    
    init(readOnlyValue: Int, readWriteValue: Int) {
        self.readOnlyOutside = readOnlyValue
        self.readWriteOutside = readWriteValue
    }
    
    func updateReadOnlyValue(newValue: Int) {
        // This method can change readOnlyOutside's value within the class.
        self.readOnlyOutside = newValue
    }
}

let instance = SomeClass(readOnlyValue: 5, readWriteValue: 10)

// Read-Only Outside
print(instance.readOnlyOutside) // Allowed, prints 5
// instance.readOnlyOutside = 15 // Not allowed, setter is private

// Read-Write Outside
print(instance.readWriteOutside) // Allowed, prints 10
instance.readWriteOutside = 20 // Allowed, changes the value to 20
print(instance.readWriteOutside) // Allowed, prints 20

instance.updateReadOnlyValue(newValue: 30) // Allowed, changes the value from 5 to 30
print(instance.readOnlyOutside) // Allowed, print 30

Here is an Objective C implementation:

//  MyObjectiveCClass.h

#import <Foundation/Foundation.h>

@interface MyObjectiveCClass : NSObject

@property (nonatomic, readonly) NSInteger readOnlyOutside;
@property (nonatomic) NSInteger readWriteOutside;

- (instancetype)initWithReadOnlyValue:(NSInteger)readOnlyValue readWriteValue:(NSInteger)readWriteValue;
- (void)updateReadOnlyValue:(NSInteger)newValue;

@end

//  MyObjectiveCClass.m

#import "MyObjectiveCClass.h"

@interface MyObjectiveCClass ()

@property (nonatomic, readwrite) NSInteger readOnlyOutside; // Private readwrite redeclaration

@end

@implementation MyObjectiveCClass

- (instancetype)initWithReadOnlyValue:(NSInteger)readOnlyValue readWriteValue:(NSInteger)readWriteValue {
    self = [super init];
    if (self) {
        _readOnlyOutside = readOnlyValue;
        _readWriteOutside = readWriteValue;
    }
    return self;
}

- (void)updateReadOnlyValue:(NSInteger)newValue {
    _readOnlyOutside = newValue;
}

@end

// How to use

MyObjectiveCClass *instance = [[MyObjectiveCClass alloc] initWithReadOnlyValue:5 readWriteValue:10];
    
// Read-Only Outside
NSLog(@"%ld", (long)instance.readOnlyOutside); // Allowed, prints 5
// instance.readOnlyOutside = 15; // Not allowed, setter is private
    
// Read-Write Outside
NSLog(@"%ld", (long)instance.readWriteOutside); // Allowed, prints 10
instance.readWriteOutside = 20; // Allowed, changes the value to 20
NSLog(@"%ld", (long)instance.readWriteOutside); // Allowed, prints 20
    
[instance updateReadOnlyValue:30]; // Allowed, changes the value from 5 to 30
NSLog(@"%ld", (long)instance.readOnlyOutside); // Allowed, prints 30