Reuse one frozen object per depth for a nested None

changes/cache-nested-none-markers.polish.md

@@ -0,0 +1 @@
+- Reuse one object per depth for nested `None` (`Some(None)`, `Some(Some(None))`, …), so creating one no longer allocates and `Some(None) === Some(None)` holds.

packages/@rescript/runtime/Primitive_option.res

@@ -13,12 +13,32 @@ let isNested = (x: Obj.t): bool => {
   Obj.repr((Obj.magic(x): nested).depth) !== Obj.repr(Primitive_js_extern.undefined)
 }
 
+external getUnsafe: (array<'a>, int) => 'a = "%array_unsafe_get"
+external setUnsafe: (array<'a>, int, 'a) => unit = "%array_unsafe_set"
+@scope("Object") external freeze: nested => nested = "freeze"
+
+/* One frozen representation per depth, created on first use, so that
+   wrapping and unwrapping a nested [None] does not allocate and
+   [Some(None) === Some(None)] holds */
+let markers: array<nested> = []
+
+let marker = (depth: int): Obj.t => {
+  let m = getUnsafe(markers, depth)
+  if Obj.repr(m) !== Obj.repr(Primitive_js_extern.undefined) {
+    Obj.repr(m)
+  } else {
+    let m = freeze({depth: depth})
+    setUnsafe(markers, depth, m)
+    Obj.repr(m)
+  }
+}
+
 let some = (x: Obj.t): Obj.t =>
   if Obj.magic(x) == None {
-    Obj.repr({depth: 0})
+    marker(0)
   } /* [x] is neither None nor null so it is safe to do property access */
   else if x !== Obj.repr(Primitive_js_extern.null) && isNested(x) {
-    Obj.repr({depth: (Obj.magic(x): nested).depth + 1})
+    marker((Obj.magic(x): nested).depth + 1)
   } else {
     x
   }
@@ -48,7 +68,7 @@ let valFromOption = (x: Obj.t): Obj.t =>
     if depth == 0 {
       Obj.magic(None)
     } else {
-      Obj.repr({depth: depth - 1})
+      marker(depth - 1)
     }
   } else {
     Obj.magic(x)

packages/@rescript/runtime/lib/es6/Primitive_option.mjs

@@ -5,15 +5,25 @@ function isNested(x) {
   return x.BS_PRIVATE_NESTED_SOME_NONE !== undefined;
 }
 
+let markers = [];
+
+function marker(depth) {
+  let m = markers[depth];
+  if (m !== undefined) {
+    return m;
+  }
+  let m$1 = Object.freeze({
+    BS_PRIVATE_NESTED_SOME_NONE: depth
+  });
+  markers[depth] = m$1;
+  return m$1;
+}
+
 function some(x) {
   if (x === undefined) {
-    return {
-      BS_PRIVATE_NESTED_SOME_NONE: 0
-    };
+    return marker(0);
   } else if (x !== null && x.BS_PRIVATE_NESTED_SOME_NONE !== undefined) {
-    return {
-      BS_PRIVATE_NESTED_SOME_NONE: x.BS_PRIVATE_NESTED_SOME_NONE + 1 | 0
-    };
+    return marker(x.BS_PRIVATE_NESTED_SOME_NONE + 1 | 0);
   } else {
     return x;
   }
@@ -43,9 +53,7 @@ function valFromOption(x) {
   if (depth === 0) {
     return;
   } else {
-    return {
-      BS_PRIVATE_NESTED_SOME_NONE: depth - 1 | 0
-    };
+    return marker(depth - 1 | 0);
   }
 }
 

packages/@rescript/runtime/lib/js/Primitive_option.cjs

@@ -5,15 +5,25 @@ function isNested(x) {
   return x.BS_PRIVATE_NESTED_SOME_NONE !== undefined;
 }
 
+let markers = [];
+
+function marker(depth) {
+  let m = markers[depth];
+  if (m !== undefined) {
+    return m;
+  }
+  let m$1 = Object.freeze({
+    BS_PRIVATE_NESTED_SOME_NONE: depth
+  });
+  markers[depth] = m$1;
+  return m$1;
+}
+
 function some(x) {
   if (x === undefined) {
-    return {
-      BS_PRIVATE_NESTED_SOME_NONE: 0
-    };
+    return marker(0);
   } else if (x !== null && x.BS_PRIVATE_NESTED_SOME_NONE !== undefined) {
-    return {
-      BS_PRIVATE_NESTED_SOME_NONE: x.BS_PRIVATE_NESTED_SOME_NONE + 1 | 0
-    };
+    return marker(x.BS_PRIVATE_NESTED_SOME_NONE + 1 | 0);
   } else {
     return x;
   }
@@ -43,9 +53,7 @@ function valFromOption(x) {
   if (depth === 0) {
     return;
   } else {
-    return {
-      BS_PRIVATE_NESTED_SOME_NONE: depth - 1 | 0
-    };
+    return marker(depth - 1 | 0);
   }
 }
 

tests/tests/src/option_nested_marker_test.mjs

@@ -0,0 +1,72 @@
+// Generated by ReScript, PLEASE EDIT WITH CARE
+
+import * as Mocha from "mocha";
+import * as Test_utils from "./test_utils.mjs";
+import * as Primitive_object from "@rescript/runtime/lib/es6/Primitive_object.mjs";
+import * as Primitive_option from "@rescript/runtime/lib/es6/Primitive_option.mjs";
+
+function wrap(x) {
+  return Primitive_option.some(x);
+}
+
+function unwrap(x) {
+  if (x !== undefined) {
+    return Primitive_option.valFromOption(x);
+  }
+  throw {
+    RE_EXN_ID: "Assert_failure",
+    _1: [
+      "option_nested_marker_test.res",
+      11,
+      12
+    ],
+    Error: new Error()
+  };
+}
+
+function depth(x) {
+  if (x === undefined) {
+    return 0;
+  }
+  let match = Primitive_option.valFromOption(x);
+  if (match !== undefined) {
+    if (Primitive_option.valFromOption(match) !== undefined) {
+      return 3;
+    } else {
+      return 2;
+    }
+  } else {
+    return 1;
+  }
+}
+
+Mocha.describe("Option_nested_marker_test", () => {
+  Mocha.test("a nested None is the same object at each depth", () => {
+    Test_utils.eq("File \"option_nested_marker_test.res\", line 25, characters 7-14", true, Primitive_option.some(undefined) === Primitive_option.some(undefined));
+    Test_utils.eq("File \"option_nested_marker_test.res\", line 26, characters 7-14", true, Primitive_option.some(Primitive_option.some(undefined)) === Primitive_option.some(Primitive_option.some(undefined)));
+    Test_utils.eq("File \"option_nested_marker_test.res\", line 27, characters 7-14", false, Primitive_option.some(undefined) === Primitive_option.some(Primitive_option.some(undefined)));
+  });
+  Mocha.test("unwrapping gives the marker one level down", () => {
+    Test_utils.eq("File \"option_nested_marker_test.res\", line 31, characters 7-14", true, unwrap(Primitive_option.some(Primitive_option.some(undefined))) === Primitive_option.some(undefined));
+    Test_utils.eq("File \"option_nested_marker_test.res\", line 32, characters 7-14", true, unwrap(unwrap(Primitive_option.some(Primitive_option.some(undefined)))) === undefined);
+  });
+  Mocha.test("markers are frozen", () => {
+    Test_utils.eq("File \"option_nested_marker_test.res\", line 36, characters 7-14", true, Object.isFrozen(Primitive_option.some(undefined)));
+    Test_utils.eq("File \"option_nested_marker_test.res\", line 37, characters 7-14", true, Object.isFrozen(Primitive_option.some(Primitive_option.some(undefined))));
+  });
+  Mocha.test("matching and equality are unchanged", () => {
+    Test_utils.eq("File \"option_nested_marker_test.res\", line 42, characters 7-14", 0, depth(undefined));
+    Test_utils.eq("File \"option_nested_marker_test.res\", line 43, characters 7-14", 1, depth(Primitive_option.some(undefined)));
+    Test_utils.eq("File \"option_nested_marker_test.res\", line 44, characters 7-14", 2, depth(Primitive_option.some(Primitive_option.some(undefined))));
+    Test_utils.eq("File \"option_nested_marker_test.res\", line 45, characters 7-14", 3, depth(Primitive_option.some(Primitive_option.some(1))));
+    Test_utils.eq("File \"option_nested_marker_test.res\", line 46, characters 7-14", Primitive_option.some(Primitive_option.some(undefined)), Primitive_option.some(Primitive_option.some(undefined)));
+    Test_utils.eq("File \"option_nested_marker_test.res\", line 47, characters 7-14", true, Primitive_object.equal(Primitive_option.some(Primitive_option.some(undefined)), Primitive_option.some(Primitive_option.some(undefined))));
+  });
+});
+
+export {
+  wrap,
+  unwrap,
+  depth,
+}
+/*  Not a pure module */

tests/tests/src/option_nested_marker_test.res

@@ -0,0 +1,49 @@
+open Mocha
+open Test_utils
+
+@scope("Object") external isFrozen: 'a => bool = "isFrozen"
+
+let wrap = x => Some(x)
+
+let unwrap = (x: option<'a>) =>
+  switch x {
+  | Some(v) => v
+  | None => assert(false)
+  }
+
+let depth = (x: option<option<option<int>>>) =>
+  switch x {
+  | None => 0
+  | Some(None) => 1
+  | Some(Some(None)) => 2
+  | Some(Some(Some(_))) => 3
+  }
+
+describe(__MODULE__, () => {
+  test("a nested None is the same object at each depth", () => {
+    let none: option<int> = None
+    eq(__LOC__, true, wrap(none) === wrap(none))
+    eq(__LOC__, true, wrap(wrap(none)) === wrap(wrap(none)))
+    eq(__LOC__, false, wrap(none) === Obj.magic(wrap(wrap(none))))
+  })
+  test("unwrapping gives the marker one level down", () => {
+    let none: option<int> = None
+    eq(__LOC__, true, unwrap(wrap(wrap(none))) === wrap(none))
+    eq(__LOC__, true, unwrap(unwrap(wrap(wrap(none)))) === none)
+  })
+  test("markers are frozen", () => {
+    let none: option<int> = None
+    eq(__LOC__, true, isFrozen(wrap(none)))
+    eq(__LOC__, true, isFrozen(wrap(wrap(none))))
+  })
+  test("matching and equality are unchanged", () => {
+    let none: option<int> = None
+    let none2: option<option<int>> = None
+    eq(__LOC__, 0, depth(None))
+    eq(__LOC__, 1, depth(wrap(none2)))
+    eq(__LOC__, 2, depth(wrap(wrap(none))))
+    eq(__LOC__, 3, depth(wrap(wrap(Some(1)))))
+    eq(__LOC__, Some(Some(None)), wrap(wrap(none)))
+    eq(__LOC__, true, wrap(wrap(none)) == Some(Some(None)))
+  })
+})