gistfile1.txt

/// PrintIt.swift
@objcMembers public class PrintIt: NSObject {
	func printIt(_ dict: [String : String]) {
		print(dict)
	}
}

/// ViewController.m

#import <PrintIt-Swift.h>

- (void)viewDidLoad {
	[super viewDidLoad];
	// Do any additional setup after loading the view.
	
	NSMutableDictionary *nonStrings = [NSMutableDictionary new];
	[nonStrings setObject:@100 forKey:@"Steve"];
  PrintIt *p = [PrintIt new];
	[p printIt:nonStrings];
}

/// Result
SIGABRT
Could not cast value of type '__NSCFNumber' (0x7fff86d3d610) to 'NSString' (0x7fff86d63d00).
2020-10-30 18:52:44.553678-0700 PrintIt[31294:380864] Could not cast value of type '__NSCFNumber' (0x7fff86d3d610) to 'NSString' (0x7fff86d63d00)