How to efficiently wrap a C-library into Swift class - objective-c

Question

I want to wrap a C-library (handling some NumberTheory related items, which I wrote some 20 years ago in C) into Swift. I started writing an Objective-C wrapper for this C-library, end then wrote a Swift derived class from the Objective-C wrapper.
Since Objective-C doesn't allow me to write overloaded methods/operators, I want to accomplish this in Swift. The C-library in question has API-calls starting with 'numthe' and a libnumthe.a and a "numthe.h" include file. The Objective-C wrapper/class is called NumTheObjC and the Swift class NumThe
Currently I've the following code for the NumTheObjC.h file:
#import <Foundation/Foundation.h>
#import <stdio.h>
#import "numthe.h"
#interface NumTheObjC : NSObject
{
numthe_prime nPrime; // Holds a numthe_prime number type instance.
numthe_perfect nPerfect; // Holds a numthe_perfect number type instance.
//... more numthe types/structure instances here.
}
-(id)init; // Default initializer
-(id)init:(NSString *)str; // Initialize from string-value.
-(void)add:(NumTheObjC *)op; // a += b
+(NumTheObjC *)add:(NumTheObjC *)left right:(NumTheObjC *)right; // x = a + b
-(void)setFromInt:(signed int)nrInt; // Initialize/set from int.
-(void)setFromLong:(signed long)nrLong; // Initialize/set from long.
-(void)setFromUInt:(unsigned int)nrUInt; // Initialize/set from uint.
-(void)setFromULong:(unsigned long)nrULong; // Initialize/set from ulong.
#end
And for the Swift wrapper I came up with the NumThe.swift file:
class NumThe : NumTheObjC {
init(nr: Int) {
super.init()
setFromInt(nr)
}
init(nr: UInt) {
super.init()
setFromUInt(nr)
}
init(strNr: String) {
super.init(strNr)
}
//... more overloaded 'constructors/initializers here ...
}
//-- Overloaded operator a + b
func + (inout left: NumThe, right: NumThe) -> NumTheObjC {
return NumTheObjC.add(left, right: right)
}
//-- Overloaded operator +=
func += (inout left: NumTheObjC, right: NumThe) {
return left.add(right)
}
Still some thoughts and questions remain, viz.:
1. I'm wondering if the above is the best approach to accomplish my goal.
2. Should the signature of all methods use NumTheObjC parameter-types instead of NumThe?
3. I can't seem to figure out how to let the above overloaded operator for 'a + b' return a NumThe instance instead of the NumTheObjC-instance.
4. Is there a more efficient approach in using C++ like templates/types to get all kinds of overloaded methods/operators?
Thanks in advance for any suggestions/tips!

Answer 1

1. I'm wondering if the above is the best approach to accomplish my goal.
You can need a new subclass NumThe. You can add new init() via extension of NumTheObjC. See this Apple doc for more info
2. Should the signature of all methods use NumTheObjC parameter-types instead of NumThe?
If you use extension then you do not need to change your parameter types
3. I can't seem to figure out how to let the above overloaded operator for 'a + b' return a NumThe instance instead of the NumTheObjC-instance.
Solution for point 1 ('extension') should resolve this too
4. Is there a more efficient approach in using C++ like templates/types to get all kinds of overloaded methods/operators?
I don't think it is possible. Again check out this Apple doc, the Preprocessor Directives section.