Add Required system param

[TheRawMeatball]

Adds an alternative to Local without a FromWorld bound.

[alice-i-cecile]

Looks interesting. What do you see this being used for?

[Ratysz]

Any situation where the local resource cannot be initialized automatically, and anytime say a plugin author wants to draw attention to a local resource being configurable.

[NathanSWard]

Looks pretty good, however, I'm not so sure about the name Required.
Perhaps:
Configured
(can't really think of any others haha)

Or, would it be possible to overload the usage of Local either via a second generic type or trait which can statically change behavior?

Maybe like
Configured<Local<T>> or something like that? 🤷

[alice-i-cecile]

My preference is definitely to override or extend Local in some way; the usage of the two APIs is identical except at initialization.

I suppose there's no way to default to this behaviour if FromWorld is missing?

[cart]

I suppose there's no way to default to this behaviour if FromWorld is missing?

Specialization could probably make this work, but without it i'm pretty this is impossible if we want FromWorld to be "automatic" behavior.

We could remove the FromWorld constraint and make Local always require manual configuration, but that would be a pretty huge step down in usability.

[mockersf]

Not a fan of having both Local and Required, or the fact that Required would fail only at runtime...

But I would love to have something that fails to compile without a .config() call...

[cart]

If we're going to have another type for this, I think Configured is the best name so far. It guides the user toward the "config()" api and semi-implies that if you don't "configure" it, something bad might happen.

[Nilirad]

• About naming: I like Configured. I had a hard time figuring out the meaning from Required.
• About the feature: Could this help seeding multiple system local PRNGs from a single seed generator, as described in Add random number generator resource (optionally specified with a seed) #2355?

[Ratysz]

+1 to Configured.

But I would love to have something that fails to compile without a .config() call...

I low-key assumed that was already the case when skimming it. Hm.

Could this help seeding multiple system local PRNGs from a single seed generator [...]

Not any more than Local itself could.

[mockersf]

Would it be possible to have a const generic to specify if the Local need configuration?

struct Local<const DEFAULT: bool>;

fn init<const DEFAULT: bool>(test: Local<DEFAULT>) {
    if DEFAULT {
        println!("using default");
    } else {
        println!("need configuration");
    }
}

But I would love to have something that fails to compile without a .config() call...

I low-key assumed that was already the case when skimming it. Hm.

Didn't check, but it's an expect so that should fail at runtime

[inodentry]

OK, so I just had a real-world use case for what this PR proposes. See: https://discord.com/channels/691052431525675048/742884593551802431/864264371106742312

[mockersf]

I played with the const generic option in #2463, it works but I think it's not pretty in current Rust

[TheRawMeatball]

Closing because better patterns exist.