breaking: rename svelte/reactivity helpers to include Svelte prefix

[trueadm]

After discussing this topic internally, we agree that we should rename the reactivity helpers. Rather than having a Reactive* prefix we instead decided on Svelte* prefix, as it would make it clearer that these are specifically for Svelte.

• Map becomes SvelteMap
• Set becomes SvelteSet
• Date becomes SvelteDate
• URL becomes SvelteURL

Closes #12192

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[Rich-Harris]

We should keep the old exports around for now, mark them as deprecated, and have them throw a useful error when you try to use them. Otherwise this will be a cryptic breaking change for existing users of these classes

[Conduitry]

We can mark the exports as deprecated for the benefit of intellisense, but we shouldn't use the term "deprecated" in the error messages that are thrown - these aren't deprecated, they don't work at all anymore.

[trueadm]

We can mark the exports as deprecated for the benefit of intellisense, but we shouldn't use the term "deprecated" in the error messages that are thrown - these aren't deprecated, they don't work at all anymore.

Good point. tweaked.

[joshnuss]

Just a thought: Would you consider prefixing them with $ instead of Svelte?

For example $Map(), $Set()

That would keep the prefix in line with other runes

[trueadm]

Just a thought: Would you consider prefixing them with $ instead of Svelte?

For example $Map(), $Set()

That would keep the prefix in line with other runes

They aren't runes though?

[joshnuss]

Sorry incorrect wording, I meant to keep the naming similar to other reactivity primitives.

First contact with the naming felt slightly odd to me (though to be fair, that happens sometimes with new things)

I feel it would be easier to explain that "a Map isn't reactive, but a $Map is reactive", every time you see a dollar sign, it's reactive.

Also prefixing objects with the name of the framework just felt funny to me. (just an opinion, trying to help keep things simple)

[trueadm]

@joshnuss That's not consistent though. If you create a custom class that has reactive fields, it doesn't have a dollar prefix either, even if it is reactive. The dollar prefix is for runes only (and I guess stores) and thus is a compiler hint that something is special – it does not mean that something is reactive. So, I don't think adding a prefix to Map or Set etc will benefit anything here, just make things more complicated.

[joshnuss]

Ok no worries!
Thanks for your time