Wrap a reader and optional writer as a callable

Builds a callable proxy from a 0-arg get reader and an optional 1-arg set writer. The proxy is itself a callable: proxy() invokes get(), proxy(value) invokes set(value). Auto-bind treats the proxy like any other callable, so it composes with value and checked props without any special handling.

Usage

reactiveProxy(get, set = NULL)

Arguments

get

A 0-arg callable returning the read value. Typically a reactiveVal, a reactiveStore leaf, another reactiveProxy, or a closure like \() transform(rv()).

set

A 1-arg function called with the incoming value on write, or NULL for a read-only proxy. Defaults to NULL.

Value

A callable with class c("reactiveProxy", "reactive", "function").

Details

set is a side-effectful handler, not a pure transform. It receives the incoming value and decides what to do — write to a target, write a transformed value, set an error flag, trigger a side effect, or drop the write entirely. Because set is a closure, it can read sibling state for cross-field validation.

Pass set = NULL (or omit it) to make the proxy read-only — writes are silently dropped. With auto-bind, this lets the input snap back to the current value via the optimistic-update protocol.

Proxies compose: a proxy is itself a callable (0-arg → get, 1-arg → set), so another reactiveProxy can use it as either its get or its set.