I'm looking at the dub package format [1] about optional dependencies and it says:

"With this set to true, the dependency will only be used if explicitly selected in dub.selections.json. If omitted, this attribute defaults to false."

And it occurs to me that I don't know anything about how dub.selections.json works.

I would think dub optional dependencies work such that if there are no functions being called/compiled that import an optional dependency, then the dependency wouldn't be included. How is it different from dmd -i?

The dub.selections.json in some of my projects look like a listing of the dependencies and their versions. Above should imply that the optional dependency would only get included there if the import is actually used somewhere in the project. Is that correct?

[1] https://dub.pm/package-format-json.html

On 2/24/23 2:01 PM, jmh530 wrote:

Let's say you have dependency A, which has an optional dependency on B.

In your project, if you depend on A, but don't explicitly depend on B, then A will be built without B as a dependency.

If you have a dependency on A and B, then B's optional dependency will kick in, and participate in the selection of it's version.

So for instance, you could depend on B version 1 or higher, and the optional dependency could be on v1.5 or higher, it will select the highest version of 1.5

dub.selections.json only applies to the primary project. So the decision on which versions of which dependencies to use is decided by the whole tree.

-Steve

On Friday, 24 February 2023 at 19:37:41 UTC, Steven Schveighoffer wrote:

Ok this makes sense. So it's all about dependencies downstream. For instance, if I list B as a dependency in my project but never use it in my own project, it will still compile in (so for instance if A's functionality differs depending on if B is included, then I will get that functionality even if I don't use B directly in my project).