Fix fromDataView: enumerable, complete comment, optional setter, readonly inference

deno.json

@@ -1,6 +1,6 @@
 {
   "name": "@rotu/structview",
-  "version": "0.14.1",
+  "version": "0.15.0",
   "license": "MIT",
   "tasks": {
     "dev": "deno test --watch",

fields.ts

@@ -273,13 +273,36 @@ export function bool(fieldOffset: number): StructPropertyDescriptor<boolean> {
 
 /**
  * Define a descriptor based on a dataview of the struct
- * @param fieldGetter function which, given a dataview, returns
- * @returns
+ * @param fieldGetter function which, given a dataview, returns the field value
+ * @param fieldSetter optional function which, given a dataview and a value, sets the field value
+ * @returns an enumerable property descriptor; readonly if no setter is provided
  */
 export function fromDataView<T>(
   fieldGetter: (dv: DataView) => T,
-): StructPropertyDescriptor<T> & ReadOnlyAccessorDescriptor<T> {
+  fieldSetter: (dv: DataView, value: T) => void,
+): StructPropertyDescriptor<T>
+export function fromDataView<T>(
+  fieldGetter: (dv: DataView) => T,
+): StructPropertyDescriptor<T> & ReadOnlyAccessorDescriptor<T>
+export function fromDataView<T>(
+  fieldGetter: (dv: DataView) => T,
+  fieldSetter?: (dv: DataView, value: T) => void,
+): StructPropertyDescriptor<T> {
+  if (fieldSetter !== undefined) {
+    return {
+      enumerable: true,
+      get() {
+        const dv = structDataView(this)
+        return fieldGetter(dv)
+      },
+      set(value) {
+        const dv = structDataView(this)
+        fieldSetter(dv, value)
+      },
+    }
+  }
   return {
+    enumerable: true,
     get() {
       const dv = structDataView(this)
       return fieldGetter(dv)

mod_test.ts

@@ -5,6 +5,7 @@ import {
   f16,
   f32,
   f64,
+  fromDataView,
   i16,
   i32,
   i64,
@@ -449,3 +450,49 @@ Deno.test("alloc", () => {
   // ensure correct typing (that alloc doesn't return a bare Struct)
   const _zz: Sized = z
 })
+
+Deno.test("fromDataView getter-only is readonly and enumerable", () => {
+  class S extends defineStruct({
+    val: fromDataView((dv) => dv.getUint8(0)),
+  }) {}
+  const buf = new Uint8Array([42])
+  const obj = new S(buf)
+  assertEquals(obj.val, 42)
+
+  // type test: val is readonly
+  assertThrows(() => {
+    // @ts-expect-error assigning to readonly property
+    obj.val = 1
+  })
+
+  // the descriptor should be enumerable
+  const keys: string[] = []
+  for (const k in S.prototype) {
+    keys.push(k)
+  }
+  assert(keys.includes("val"))
+})
+
+Deno.test("fromDataView with setter is writable and enumerable", () => {
+  class S extends defineStruct({
+    val: fromDataView(
+      (dv) => dv.getUint8(0),
+      (dv, v) => dv.setUint8(0, v),
+    ),
+  }) {}
+  const buf = new Uint8Array([0])
+  const obj = new S(buf)
+  obj.val = 99
+  assertEquals(obj.val, 99)
+  assertEquals(buf[0], 99)
+
+  // type test: val is writable (no @ts-expect-error needed)
+  const _: number = obj.val
+
+  // the descriptor should be enumerable
+  const keys: string[] = []
+  for (const k in S.prototype) {
+    keys.push(k)
+  }
+  assert(keys.includes("val"))
+})