A struct's dyn view takes .field and [:k], read and assigned, and a get on it traps at its own site.

runtime/flan_dyn.c

@@ -3733,6 +3733,12 @@ flan_dyn flan_dyn_get(flan_dyn m, flan_dyn k, const uint8_t *loc,
                       int64_t loclen) {
   class_entry *e;
   if (!is_map(m)) trap2(loc, loclen, TYPE_TRAP, "get", "only a map answers it", m, k);
+  /* A struct's view: its field, or a trap at this site naming the fields. */
+  if (dyn_obj(m)->kind == OBJ_VIEW) {
+    const uint8_t *fty;
+    uint8_t *p = view_field(loc, loclen, "get", dyn_obj(m), k, &fty);
+    return view_read(loc, loclen, "get", dyn_obj(m), fty, p);
+  }
   e = class_sync(dyn_obj(m));
   if (e != NULL && class_slot(e, k) < 0)
     trap_no_slot(loc, loclen, "get", dyn_obj(m), e, k);

test/programs/dyn-view-any.flan

@@ -160,6 +160,19 @@
         (let [p (Point {.x 1.0 .y 2})
               q (Point {.x 1.0 .y 2})]
           (println (= (keep p) (keep q))))
+        ;; .field and [:k] on a struct's view: a read is get, a set is put,
+        ;; and the typed struct sees every write.
+        (let [p (Point {.x 1.0 .y 2})
+              m (Mix {.a 1 .b 2 .c 0.5 .d false .e [1 2 3] .f 4})
+              dp (keep p)
+              dm (keep m)]
+          (set (.y dp) 5)
+          (update (.y dp) + 10)
+          (set (at dp :x) 2.5)
+          (set (.d dm) true)
+          (set (at (.e dm) 1) 20)
+          (println (.y dp) (at dp :x) (.a dm) (.d dm) (at (.e dm) 1))
+          (println (.y p) (.x p) (.d m) (at (.e m) 1)))
         0)
       ;; A value an element's width cannot hold.
       (= n 1)
@@ -215,4 +228,9 @@
       (let [fs [(f32 0.5)]]
         (set (at (keep fs) 0) 16777217)
         0)
+      ;; A field a struct does not have, through .field.
+      (= n 10)
+      (let [p (Point {.x 1.0 .y 2})]
+        (set (.z (keep p)) 3)
+        0)
       :else (do (println "?") 1))))

test/test_acceptance.ml

@@ -5925,7 +5925,8 @@ level "1"
        grid [[1 2 3] [4 5 60]]\n60\n\
        points [#Point{:x 1 :y 1} #Point{:x 2 :y 20}]\n20\n\
        vec [1 2 3]\n3\n6\n5\n4\n3\n\
-       temp #Point{:x 1.5 :y 2}\n4\n3\ntrue\n"
+       temp #Point{:x 1.5 :y 2}\n4\n3\ntrue\n\
+       15 2.5 1 true 20\n15 2.5 true 20\n"
     in
     let any_traps =
       [ ("1", "300 does not fit a u8 element, which holds 0 to 255");
@@ -5933,7 +5934,8 @@ level "1"
                dyn int");
         ("3", "a Point has no field :z. Its fields are :x :y");
         ("8", "a str element is read-only through a dyn view");
-        ("9", "16777217 has no exact f32") ]
+        ("9", "16777217 has no exact f32");
+        ("10", "dyn put: a Point has no field :z. Its fields are :x :y") ]
     and any_stale =
       [ ("4", "this view points into a local of leak-local, and that call \
                has returned");