For computed properties, change the way dependencies are specified

[tinius]

Hi,

I was very surprised when I found out today that in the computed object, the dependencies for each computed property are identified by the names of the parameters passed into the respective functions. This seems to be at odds with what I thought was a common principle in JS, namely that I can call my parameters whatever I want in the function head and worry about what is passed in elsewhere. I guess another problem with the current design of computed is that you can't dynamically determine the dependencies of a property.

May I ask what the rationale behind this is? I believe a more intuitive approach would be to specify dependencies in the form of a list of (string) keys, similar to how component.observe works for example.

[Conduitry]

Having the computed property dependencies be fixed makes them able to be analyzed at compile time, so that Svelte can output code to recompute only the computed properties that might have changed. As for the syntax, it is a bit magical, but provides a very succinct way of declaratively specifying these dependencies.

If you have a problem that is more general than computed properties can solve, a reasonable solution would probably be to just attach some .observe handlers to the component in its oncreate hook.

[Crisfole]

Can this be closed in light of #1069 ? I believe they address the same issue.

[arxpoetica]

Closing with ongoing discussion about destructured syntax. (See #1069)