Objective-C bounded LRU cache with timestamp recency

#import <Foundation/Foundation.h>

static id LRUGet(NSMutableDictionary *cache, NSString *key) {
    NSDictionary *entry = cache[key];
    if (!entry) return nil;
    entry = @{@"value": entry[@"value"], @"used": @([[NSDate date] timeIntervalSince1970])};
    cache[key] = entry;
    return entry[@"value"];
}

static void LRUPut(NSMutableDictionary *cache, NSString *key, id value, NSUInteger limit) {
    cache[key] = @{@"value": value ?: [NSNull null], @"used": @([[NSDate date] timeIntervalSince1970])};
    while (cache.count > limit) {
        NSString *oldest = [cache keysSortedByValueUsingComparator:^NSComparisonResult(NSDictionary *a, NSDictionary *b) {
            return [a[@"used"] compare:b[@"used"]];
        }].firstObject;
        [cache removeObjectForKey:oldest];
    }
}