Getting around Swift 2’s lack of compatibility with vararg methods for complication text providers.

CLKTextProvider+NNNCompoundTextProviding.h

@interface CLKTextProvider (NNNCompoundTextProviding)

+ (nonnull CLKTextProvider *)nnn_textProviderByJoiningProvider:(nonnull CLKTextProvider *)provider1 andProvider:(nonnull CLKTextProvider *)provider2 withString:(nullable NSString *)joinString;

@end

CLKTextProvider+NNNCompoundTextProviding.m

@implementation CLKTextProvider (NNNCompoundTextProviding)

+ (nonnull CLKTextProvider *)nnn_textProviderByJoiningProvider:(nonnull CLKTextProvider *)provider1 andProvider:(nonnull CLKTextProvider *)provider2 withString:(nullable NSString *)joinString
{
    NSString *textProviderToken = @"%@";
    
    NSString *formatString;
    
    if (joinString != nil) {
        formatString = [NSString stringWithFormat:@"%@%@%@",
                        textProviderToken,
                        joinString,
                        textProviderToken];
    }
    else {
        formatString = [NSString stringWithFormat:@"%@%@",
                        textProviderToken,
                        textProviderToken];
    }
    
    return [self textProviderWithFormat:formatString, provider1, provider2];
}

@end

let text1 = CLKSimpleTextProvider(text: "red")
text1.tintColor = .red

let text2= CLKSimpleTextProvider(text: "green")
text2.tintColor = .green

// secret sauce:
// just pass CLKTextProvider objects as arguments
let finalText = CLKTextProvider(format: "%@ and %@", text1, text2)

Thank you very much! Just wanted to add how to use it with CLKRelativeDateTextProvider:

let myComplicationTemplate = CLKComplicationTemplateUtilitarianLargeFlat()
let dateProvider = CLKRelativeDateTextProvider()

dateProvider.date = Date()
dateProvider.calendarUnits = [.hour, .minute]
dateProvider.relativeDateStyle = .naturalAbbreviated

let finalText = CLKTextProvider(format: "GBT * %@", dateProvider)

myComplicationTemplate.textProvider = finalText