Expose owned R vector storage as a mutable JavaScript view

Creates a fixed-length array-like JavaScript object whose indexed writes update R-owned vector storage. The wrapper makes one copy when it is created; passing it to JavaScript does not copy or convert the complete vector.

Usage

js_mutable_view(x)

Arguments

x

An unclassed raw, logical, integer, double, or character vector.

Value

A mutable-view wrapper containing an independent copy in value.

Details

JavaScript reads convert elements on demand and writes update view$value. The caller's original vector is never modified. Multiple JavaScript views of the same wrapper share its owned storage.

The view has length, indexed access, enumeration, iteration, inherited Array methods, and toArray(). Its length cannot change, properties cannot be added, and elements cannot be deleted. Methods such as reverse, sort, fill, and copyWithin work because they only replace existing elements.

Assignments are type checked. JavaScript null and undefined write R missing values except for raw vectors. JavaScript NaN remains an ordinary R NaN. Factors, dates, and other classed vectors are rejected.

Normal R copy-on-write rules still apply. Replacing or modifying view$value in R after JavaScript retains the view can detach the R binding from the retained storage.

Examples

ctx <- JSContext$new(profile = "bare")
ctx$source(code = "function increment(x) { x[0] += 1; return x; }")
values <- js_mutable_view(c(1, 2, 3))
ctx$call("increment", values)
#> $value
#> [1] 2 2 3
#> 
#> attr(,"class")
#> [1] "quickjs_mutable_view"
values$value
#> [1] 2 2 3