Bug 17972 – __traits(getLinkage) doesn't work for classes

I'm not sure if this should be considered a bug or an enhancement request. I think that __traits(getLinkage) should work for classes, structs and interfaces. This is useful to identify a C++ class/struct or an Objective-C interface. Technically the class might not have a linkage but since one usually put the linkage on a class I think it make sense to be able to get the linkage from a class. From an implementation point of view, it looks like the original implementation [1] assumed that all declarations inherit from the Declaration class, but this is not the case for structs, classes and interfaces. [1] https://github.com/dlang/dmd/pull/6822

This is a bit complicated since you cannot get the linkage directly for aggregate declarations. The only way to obtain it is to visit the AST and search for LinkDeclarations that point out to the class/struct of interest. I wonder why structs and classes don't have a linkage property.

What about using the existing fields in ClassDeclaration: "cpp", "objc" and so on [1]? I know it's not exactly the same. [1] https://github.com/dlang/dmd/blob/master/src/ddmd/dclass.d#L215-L218

I've just run into this issue. I was trying to fix `destroy()` not working on C++ classes, and quickly realised I needed a reliable way to detect C++ classes! So, we can't fix destroy() until we have this, or an alternative accepted solution...

Fixed by : https://github.com/dlang/dmd/pull/8224 https://github.com/dlang/dmd/pull/8336