> I think the question is whether ClojureScript needs to support bound-fn
at all. But maybe it really is useful in a single-threaded environment! :)
I'm already finding it very useful for an experimental UI framework design
I'm working on. I have a dynamically bound "insert pointer", such that UI
views are functions which can be re-run automatically and "emit" dom
elements into the tree at the point they were dynamically bound. My defview
macro checks which arguments are IWatchable and triggers an inplace dom
re-render when the arguments change. I'd also like to use the analyzer to
look for deref calls, instead of just arguments, so I can get much more
finely grained change notifications. In particular, data can be pushed from
the server and trigger an asynchronous re-render, which needs to have the
insert pointer and other bindings.
> Your implementation will likely be *dramatically* slower
Hence why it only applies to ^:dynamic variables. There are generally
pretty few of these in any application.
I do, however, plan to add an additional way to trigger it for non-dynamic
variables, if you want IWatchable support, etc. Probably a ^:var metadata
attribute. {^:var false, ^:dynamic true} would be disallowed.
Also, the implementation has numerous optimization opportunities, manly
centered around using native JS objects instead of ObjMap.
> Also this seems like yet another breaking ClojureScript change.
The two breaking changes I can see:
1) binding macro
- I'm re-using the native Clojure `binding` macro, but could write a
custom one which is backwards compatible. With our without a warning
configuration.
- The behavior I have implemented matches JVM clojure: You can only use
binding on Vars labeled as ^:dynamic
- Fixing usages is as simple as adding ^:dynamic to the vars you are
binding over.
- The binding macro behavior in master is actually with-redefs, so that
could be subbed in as well.
- All and all, a pretty minimal breaking change with easy resolutions
2) ^:dynamic vars exposed to external code must now be accessed with deref
- This is extremely minor because Clojure JavaScript libraries are
generally the bottom of the stack. If you need interop, you can easily
create an additional var, or choose with-rdefs instead.
- I haven't currently implemented with-redefs because it would require
the analyzer be used to differentiate "raw" vars or vars wrapped in my Var
implementation. However, still pretty straight forward.
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