feat(exo): instance testing

packages/exo/src/exo-makers.js

@@ -88,7 +88,7 @@ export const initEmpty = () => emptyRecord;
  */
 
 /**
- * The power to amplify a live facet instance of the associated exo class kit
+ * The power to amplify a facet instance of the associated exo class kit
  * into the record of all facets of this facet instance's cohort.
  *
  * @template {any} [F=any]
@@ -97,6 +97,19 @@ export const initEmpty = () => emptyRecord;
  * @returns {F}
  */
 
+/**
+ * The power to test if a value is an instance of the
+ * associated exo class, or a facet instance of the
+ * associated exo class kit. In the later case, if a `facetName` is provided,
+ * then it tests only whether the argument is a facet instance of that
+ * facet of the associated exo class kit.
+ *
+ * @callback IsInstance
+ * @param {any} exo
+ * @param {string} [facetName]
+ * @returns {boolean}
+ */
+
 // TODO Should we split FarClassOptions into distinct types for
 // class options vs class kit options? After all, `receiveAmplifier`
 // makes no sense for normal exo classes.
@@ -129,9 +142,18 @@ export const initEmpty = () => emptyRecord;
  * definition of the exo class kit with an `Amplify` function. If called
  * during the definition of a normal exo or exo class, it will throw, since
  * only exo kits can be amplified.
- * An `Amplify` function is a function that takes a live facet instance of
+ * An `Amplify` function is a function that takes a facet instance of
  * this class kit as an argument, in which case it will return the facets
  * record, giving access to all the facet instances of the same cohort.
+ *
+ * @property {ReceivePower<IsInstance>} [receiveInstanceTester]
+ * If a `receiveInstanceTester` function is provided, it will be called
+ * during the definition of the exo class or exo class kit with an
+ * `IsInstance` function. The first argument of `IsInstance`
+ * is the value to be tested. When it may be a facet instance of an
+ * exo class kit, the optional second argument, if provided, is
+ * a `facetName`. In that case, the function tests only if the first
+ * argument is an instance of that facet of the associated exo class kit.
  */
 
 /**
@@ -169,7 +191,11 @@ export const defineExoClass = (
   options = {},
 ) => {
   harden(methods);
-  const { finish = undefined, receiveAmplifier = undefined } = options;
+  const {
+    finish = undefined,
+    receiveAmplifier = undefined,
+    receiveInstanceTester = undefined,
+  } = options;
   receiveAmplifier === undefined ||
     Fail`Only facets of an exo class kit can be amplified ${q(tag)}`;
 
@@ -202,6 +228,18 @@ export const defineExoClass = (
     return self;
   };
 
+  if (receiveInstanceTester) {
+    const isInstance = (exo, facetName = undefined) => {
+      facetName === undefined ||
+        Fail`facetName can only be used with an exo class kit: ${q(
+          tag,
+        )} has no facet ${q(facetName)}`;
+      return contextMap.has(exo);
+    };
+    harden(isInstance);
+    receiveInstanceTester(isInstance);
+  }
+
   return harden(makeInstance);
 };
 harden(defineExoClass);
@@ -229,7 +267,11 @@ export const defineExoClassKit = (
   options = {},
 ) => {
   harden(methodsKit);
-  const { finish = undefined, receiveAmplifier = undefined } = options;
+  const {
+    finish = undefined,
+    receiveAmplifier = undefined,
+    receiveInstanceTester = undefined,
+  } = options;
   const contextMapKit = objectMap(methodsKit, () => new WeakMap());
   const getContextKit = objectMap(
     contextMapKit,
@@ -268,19 +310,36 @@ export const defineExoClassKit = (
   };
 
   if (receiveAmplifier) {
-    const amplify = aFacet => {
+    const amplify = exoFacet => {
       for (const contextMap of values(contextMapKit)) {
-        if (contextMap.has(aFacet)) {
-          const { facets } = contextMap.get(aFacet);
+        if (contextMap.has(exoFacet)) {
+          const { facets } = contextMap.get(exoFacet);
           return facets;
         }
       }
-      throw Fail`Must be a facet of ${q(tag)}: ${aFacet}`;
+      throw Fail`Must be a facet of ${q(tag)}: ${exoFacet}`;
     };
     harden(amplify);
     receiveAmplifier(amplify);
   }
 
+  if (receiveInstanceTester) {
+    const isInstance = (exoFacet, facetName = undefined) => {
+      if (facetName === undefined) {
+        return values(contextMapKit).some(contextMap =>
+          contextMap.has(exoFacet),
+        );
+      }
+      assert.typeof(facetName, 'string');
+      const contextMap = contextMapKit[facetName];
+      contextMap !== undefined ||
+        Fail`exo class kit ${q(tag)} has no facet named ${q(facetName)}`;
+      return contextMap.has(exoFacet);
+    };
+    harden(isInstance);
+    receiveInstanceTester(isInstance);
+  }
+
   return harden(makeInstanceKit);
 };
 harden(defineExoClassKit);

packages/exo/test/test-amplify-heap-class-kits.js

@@ -1,4 +1,4 @@
-// modeled on test-revoke-heap-classes.js
+// modeled on test-heap-classes.js
 
 // eslint-disable-next-line import/order
 import { test } from './prepare-test-env-ava.js';

packages/exo/test/test-is-instance-heap-class-kits.js

@@ -0,0 +1,97 @@
+// modeled on test-heap-classes.js
+
+// eslint-disable-next-line import/order
+import { test } from './prepare-test-env-ava.js';
+
+// eslint-disable-next-line import/order
+import { M } from '@endo/patterns';
+import { defineExoClass, defineExoClassKit } from '../src/exo-makers.js';
+
+const UpCounterI = M.interface('UpCounter', {
+  incr: M.call().optional(M.gte(0)).returns(M.number()),
+});
+
+const DownCounterI = M.interface('DownCounter', {
+  decr: M.call().optional(M.gte(0)).returns(M.number()),
+});
+
+test('test isInstance defineExoClass', t => {
+  let isInstance;
+  const makeUpCounter = defineExoClass(
+    'UpCounter',
+    UpCounterI,
+    /** @param {number} x */
+    (x = 0) => ({ x }),
+    {
+      incr(y = 1) {
+        const { state } = this;
+        state.x += y;
+        return state.x;
+      },
+    },
+    {
+      receiveInstanceTester(i) {
+        isInstance = i;
+      },
+    },
+  );
+  t.is(isInstance(harden({})), false);
+  t.throws(() => isInstance(harden({}), 'up'), {
+    message:
+      'facetName can only be used with an exo class kit: "UpCounter" has no facet "up"',
+  });
+
+  const upCounter = makeUpCounter(3);
+
+  t.is(isInstance(upCounter), true);
+  t.throws(() => isInstance(upCounter, 'up'), {
+    message:
+      'facetName can only be used with an exo class kit: "UpCounter" has no facet "up"',
+  });
+});
+
+test('test isInstance defineExoClassKit', t => {
+  let isInstance;
+  const makeCounterKit = defineExoClassKit(
+    'Counter',
+    { up: UpCounterI, down: DownCounterI },
+    /** @param {number} x */
+    (x = 0) => ({ x }),
+    {
+      up: {
+        incr(y = 1) {
+          const { state } = this;
+          state.x += y;
+          return state.x;
+        },
+      },
+      down: {
+        decr(y = 1) {
+          const { state } = this;
+          state.x -= y;
+          return state.x;
+        },
+      },
+    },
+    {
+      receiveInstanceTester(i) {
+        isInstance = i;
+      },
+    },
+  );
+
+  t.is(isInstance(harden({})), false);
+  t.is(isInstance(harden({}), 'up'), false);
+  t.throws(() => isInstance(harden({}), 'foo'), {
+    message: 'exo class kit "Counter" has no facet named "foo"',
+  });
+
+  const { up: upCounter } = makeCounterKit(3);
+
+  t.is(isInstance(upCounter), true);
+  t.is(isInstance(upCounter, 'up'), true);
+  t.is(isInstance(upCounter, 'down'), false);
+  t.throws(() => isInstance(upCounter, 'foo'), {
+    message: 'exo class kit "Counter" has no facet named "foo"',
+  });
+});