Q:

Calling Swift code in a C testing suite

I am currently working on a library in Swift that has a version already written in C. As the version in C already has a large testing suite, I would like to just run the Swift code through the C tests.
Is it possible to call Swift in C?

A:

To call Swift from C one can wrap Swift code in Objective-C functions callable from C.  A trivial contrived example follows.
Swift code:
import Foundation

@objc public class ClassSwift : NSObject {
    public func addIntegers(int1:Int32, int2:Int32) -> Int32 {
        return int1 + int2;
    }
}

Objective-C wrapper:
// Mixed 1a is the name of my sample target
// You can see the name of your Swift header in
// Objective-C Generated Interface Header Name under Build Settings.
#import "Mixed_1a-Swift.h"

// This function is callable from C, even though it calls Swift code!
int addIntsC(int i1, int i2)
{
    ClassSwift * cs = [[ClassSwift alloc] init];
    return [cs addIntegersWithInt1:i1 int2:i2];
}

And, finally, here's the C code:
#include <stdio.h>

int addIntsC(int, int);

int main(int argc, const char * argv[]) {
    int result = addIntsC(3, 7);
    if (result == 10) puts("Test passed!");
    else puts("Failed... :(");    
    return 0;
}

