Accessing objective-c Struct from Swift

Question

I'm working on an ios application that has a mix of swift and obj-c code. One of my obj-c model classes defines a struct containing strings to assist in converting to a dictionary and back. I have the bridging header setup and I can access methods defined in my objective-c class in a swift class. What I can't figure out is how to access the static stuct to get at my property strings. Here is a snippet of my .h and .m files:

OrderItem.h

extern const struct OrderItemAttributes {
    __unsafe_unretained NSString *created;
    __unsafe_unretained NSString *created_by_id;
    __unsafe_unretained NSString *device_deleted;
} OrderItemAttributes;

@interface OrderItem : NSManagedObject {}
@property (nonatomic, strong) NSDate* created;
@end

OrderItem.m

const struct OrderItemAttributes OrderItemAttributes = {
    .created = @"created",
    .created_by_id = @"created_by_id",
    .device_deleted = @"device_deleted",
};

@implementation OrderItem
@dynamic created;
@end

I thought I would simply be able to use

OrderItem.OrderItemAttributes.created

to access the attribute strings but swift doesn't accept that syntax. Is there any way to do what I want without major changes to my objective-c code?

please, try this solution stackoverflow.com/questions/33947811/… — rkyr
– rkyr, Commented Nov 30, 2015 at 17:37
Thanks for the suggestion, but that wouldn't help in my case. I need to access the struct in swift not the other way around. — pbuchheit
– pbuchheit, Commented Nov 30, 2015 at 18:34
Possible duplicate of Access to extern const struct from Swift — pbuchheit
– pbuchheit, Commented Nov 30, 2015 at 18:45

Darren · Accepted Answer · 2015-11-30 19:05:24Z

2

The variable OrderItemAttributes isn't part of the OrderItem namespace. It would be accessed directly as:

var foo: NSString = OrderItemAttributes.created.takeUnretainedValue()

The problem you're seeing with autocomplete occurs because OrderItemAttributes is ambiguous; it's both a type name and a variable name. Use different names for the struct type name and the global variable to avoid the ambiguity. E.g., add 'Struct' to the end of the type name:

extern const struct OrderItemAttributesStruct {
    __unsafe_unretained NSString *created;
    __unsafe_unretained NSString *created_by_id;
    __unsafe_unretained NSString *device_deleted;
} OrderItemAttributes;

answered Nov 30, 2015 at 19:05

Darren

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2 Comments

TT-- Over a year ago

Why is it only visible from Swift when the __unsafe_unretained is applied? Without it results in "Cannot reference invalid declaration", same if __weak is used.

Darren Over a year ago

@TT-- Swift cannot (yet) safely track object references that are inside of a plain old C Struct, so you have to explicitly declare those references as unmanaged. That feature was only added to ObjC in 2018, and there was/is a proposal to add it to Swift as well: forums.swift.org/t/…

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