指向整数转换的不兼容指针从结果类型为“NSInteger”（又名“long”）的函数返回“id _Nullable”

Question

I want to have an object which keeps indexes of an array where id is the unique key and it's value is index ( {[id]:[index]} )

I want to dynamically return that index ie In javascript I would do something like this

const a = [{
  id: '451', 
  name: 'varun'
}]


const b = {
    '451': 0 
}

const c = '451' 

if (b[c]) return b[c] 
else return -1 

What would be it's equivalent in obj c?

Currently I am doing this

@implementation Participants {
    NSMutableDictionary *participantsKey;
}. // Equivalent to const b above


- (NSInteger)doesParticipantExist:(NSString*)id {
    if ([participantsKey valueForKey: id]) {
      return [participantsKey valueForKey: id];
    } else {
      return -1;
    }
  }

but this is throwing following warning

Incompatible pointer to integer conversion returning 'id _Nullable' from a function with result type 'NSInteger' (aka 'long')

Answer 1

valueForKey returns a nullable object 'id _Nullable' NOT an NSInteger which is a long value.

[participantsKey valueForKey: id]

Your function's return type is NSInteger and that's why it's saying it can't convert a nullable object 'id _Nullable' into NSInteger .

Here's what you can do to fix the issue.

- (NSInteger)doesParticipantExist:(NSString*)id {
    if ([participantsKey valueForKey:id]) {
        // Fix here
        return [(NSNumber*)[participantsKey valueForKey:id] integerValue];
    } else {
        return -1;
    }
}