Switch conditional block

0000-switch-block.md

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+- Start Date: 2021-4-29
+- RFC PR: 
+- Svelte Issue: 
+
+# Switch Block
+
+## Summary
+
+> This feature is a switch statement but for declaring reactive UI simmilar to `{#if}`.
+> It will behave exactly the same as a switch statement in regular programming.
+
+## Motivation
+
+> This could be useful for simple single page app that needs to switch between layouts,
+> like if you wanted a login/signup/logout/forgot password page, each page would only
+> have their own seperate elements, but not enough to warrant multiple svelte files.
+
+> It would be easier to do simple layout changes where you need to modify the layout
+> based on dynamic data and you don't want to do a large amount of `{:else if}`
+> blocks. Plus it would better describe the behaviour of what it's doing.
+
+> With switch statements you do not have to reference your varible multiple times
+> and possibly use more resources than required. That's the main benefit to
+> switch statements in programming, performance. Although with modern hardware the
+> benefits of switch statements speed are probably 1ms or less it may be beneficial
+> to lower end hardware.
+
+> My reasoning for adding this is mainly syntactic sugar (lots of else if blocks are ugly, 
+> but the performance benefits of a switch statement very are real, but very minimal.
+
+## Detailed design
+```
+{#switch *condition*} -- The default tags could be under the main switch statement, or it could be in a seperate tag as {:default}
+  <Default Content>
+{:case *constant expression*}
+  <Case specific content>
+{/switch}
+```
+
+### Technical Background
+
+> There are the standard docs for many languages such as 
+> c++ https://docs.microsoft.com/en-us/cpp/cpp/switch-statement-cpp?view=msvc-160
+> JavaScript: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/switch
+> Many languages I have seen just use the standard c syntax so there is no need to list more
+
+> React just uses normal javascript switch statements and then returns different values. https://sebhastian.com/react-switch/
+> There is a vue module which brings support for switch statements https://www.npmjs.com/package/v-switch-case
+
+### Implementation
+
+> It behaves very simmilar to `{#if}`, `{:else if}`, and `{:else}`, but
+> the conditions are static and it's backed by the switch statement of normal javascript.
+> The `{:else}` block is now in the `{#switch}` block, and the `{#if}` and `{#else if}`
+> conditions now are located in `{:case}`. I came to this after I was making a page
+> for doing various account auth related things with login, logout, signup, and reset password
+> which could all be put in one svelte file and didn't need their own files but the switch
+> statement which I use regularly in javsacript doesn't exist. So I had to use `{#else if}` blocks
+> as a bulky, inefficient stand in for a switch statement.
+
+## How we teach this
+
+> It would talk about the logic
+
+> Would the acceptance of this proposal mean the Svelte guides must be
+re-organized or altered? Does it change how Svelte is taught to new users
+at any level?
+
+> How should this feature be introduced and taught to existing Svelte
+users?
+
+## Drawbacks
+
+> The only real drawback that I could see is a very minescule bundle size increase,
+> since this is only adding on a new conditional block and not modifying a core feature
+> it most likely wont affect any current projects.
+
+> It may be confusing to some newer programmers to why you need switch statements when you
+> already have if statements.
+
+## Alternatives
+
+> Just not do this because you can already do this with relative ease, but this will
+> bring slight performance improvements to apps that use it as well as cleaner syntax.
+
+## Unresolved questions
+
+> Wether it uses `{:default}` or the default markup tags will just go below the `{#if}` statement.