CODEWITHSUNDEEP
objective-c
nugget
nugget

Reputation: 155

objective c method to return a dynamic type

I have many child-entities which inherit properties from the same BaseEntity.

I would like to write a generic method which accepts any of the children and sets the base properties. 

ChildDto *child = [[ChildDto alloc] init];
child = [BaseEntityDto SetBaseProperties:child fromDictionary:src];

The above gives the 'incompatible pointer type' error.

When I try casting the resulting BaseEntity to one of it's child classes, the cast fails and the object remains of type BaseEntity.

child = (ChildDto*)[BaseEntityDto SetBaseProperties:child fromDictionary:src];

Apparently casting is a bad idea in Objective C due to the use of pointers and there appears to be no 'dynamic' type to set as the return type.

So what's the correct way to solve this problem?

Upvotes: 0

Views: 124

Answers (3)

vikingosegundo
vikingosegundo

Reputation: 52227

If you have no reason not to do so, you should use plain inheritance to create the objects

@interface BaseEntity : NSObject
-(instancetype)initWithProperties:(NSDictionary *) properties;
@end


@implementation BaseEntity

-(instancetype)initWithProperties:(NSDictionary *) properties
{
    self = [super init];
    if (self){
         // apply properties for base
    }
    return self;
}

@end

@interface ChildDTO : BaseEntity
@end


@implementation ChildDTO

-(instancetype)initWithProperties:(NSDictionary *) properties
{
    self = [super initWithProperties:properties];
    if (self){
         // apply properties for child
    }
    return self;
}

@end

Upvotes: 1

nugget
nugget

Reputation: 155

I found that if I pass in a child of BaseEntity to SetBaseProperties, set the props and return nothing, it works. 

ChildDto *child = [[ChildDto alloc] init];
[BaseEntityDto SetBaseProperties:child fromDictionary:src];
// base properties of child are now set

So the signature for SetBaseProperties is:

+(void)SetBaseProperties:(BaseEntityDto *)object fromDictionary:(NSDictionary*)dictionary;

Is that a correct way of doing it?

Upvotes: 0

Gwendal Roué
Gwendal Roué

Reputation: 4044

Objective-C is very dynamic. Your issues may come from a lack of experience. I suggest you get familiar with the Key-Value Coding Guide: https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/KeyValueCoding/Articles/KeyValueCoding.html. It has a good chance to provide the answer to your question.

Upvotes: 0

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