Cannot put Objective-C classes in structs

[dlangBugzillaToGithub]

Jacob Carlborg (@jacob-carlborg) reported this on 2019-02-23T11:32:13Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=19694

CC List

• Walter Bright (@WalterBright)
• Adam D. Ruppe

Description

The following code fails to link with DMD 2.085.0-beta.1

extern (Objective-C) class NSObject {}

struct Foo
{
    NSObject o;
}

void main() {}

The error is:

Undefined symbols for architecture x86_64:
  "__D4main8NSObject7__ClassZ", referenced from:
      __D25TypeInfo_xC4main8NSObject6__initZ in main.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
Error: linker exited with status 1

This issue occurs due to no classinfo is outputted for Objective-C classes. This is intentional, but I'm not sure how to fix it. Global, local or TLS variables or instance variables for classes don't require the classinfo, not sure why a struct field requires it.

[dlangBugzillaToGithub]

destructionator commented on 2023-09-26T00:13:39Z

I saw this too recently, I think it is because it is trying to reference them for precise gc info.

I hacked around it by wrapping the member in a union {}

struct Foo {
    union { NSObject obj; }
}

but i agree it shouldn't require this.