osu-framework
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ppy
Allow value types to be cached and injected as dependencies
Resolves https://github.com/ppy/osu-framework/issues/6157
Consider this an RFC.
The way structs are handled right now is a mess. If I (as the person who wrote all of this) can't understand how they're handled, then I don't think anyone can. And my confusion is the result of two conflicting thought processes:
CancellationTokenis somehow a special type. How is it so?- The way I view structs is as always being initialised, whether in a "zeroed" state or otherwise (unless they're nullable).
Every value type is a special type that can only be cached by osu!framework. CancellationToken is doubly special because it sometimes arrives in load(), and sometimes doesn't, depending on whether you're in an async-load context. So the only proper way to use BDL with CancellationToken is to make it nullable.
In my opinion, if you want to cache and resolve a value-type dependency and accept whatever footguns that comes with (by-val copies, you can't cache multiple ints, etc), then you should be able to do so. But the framework should retain predictable semantics, which for me means matching the C# spec - ValueType = default! is a zero-initialised struct. This is a simplification of semantics to me.
New semantics:
Get<int>() => 0; // Allowed
Get<int?>() => null; // Allowed
Cache<int>(0); // Allowed
Cache<int>(null); // Disallowed
Cache<int?>(0); // Warning in NRT contexts
CacheAs<IInterface>(MyStruct); // Allowed - boxed.
Cache<object>(null); // Exception
Cache<object?>(null); // Exception + warning in NRT contexts
Is this something I foresee being used? No. It's just for the sake of clarifying semantics.
Why are tests failing here? I'd expect failures in the sourcegen path until a package bump or something, but the reflection path is failing too?
Sourcegen won't need updates; I just forgot to update a test. Will get to it.
Reading the OP:
Cache<int?>(0); // Warning in NRT contexts
Why would this warn? Looks like perfectly legal code to me...