Can I specify that a generic is a value type?

Question

I know that we can essentially specify that our generics be any reference type by using AnyObject:

class Foo {
    // ...
}
         


        

Answer 1

A possible way if it is enough for you to use Assertion:

public final class Synchronized {
    private var _value: T        
        
    public init(_ value: T) {
       assert(!isReferenceType(value))
       _value = value
    }
    ...
}
    
func isReferenceType(_ any: Any) -> Bool {
    return Mirror(reflecting: any).displayStyle == .class
}

Some Unit Tests to prove it works as expected:

import XCTest

final class SynchronizedTests: XCTestCase {
    class FakeClass {}
    struct FakeStruct {}
    enum FakeEnum {
        case first
    }

    func testIsReferenceType() {
        XCTAssert(isReferenceType(FakeClass()))

        XCTAssertFalse(isReferenceType(FakeStruct()))
        XCTAssertFalse(isReferenceType(FakeEnum.first))
        XCTAssertFalse(isReferenceType("string"))
        XCTAssertFalse(isReferenceType(123))
        XCTAssertFalse(isReferenceType(123.4))
        XCTAssertFalse(isReferenceType([1, 2, 3]))
        XCTAssertFalse(isReferenceType(Set([1, 2, 3])))
        XCTAssertFalse(isReferenceType(["1": 1, "2": 2, "3": 3]))
    }
}