Add RObject.class() method, tests, and update NEWS.md (#416)

NEWS.md

@@ -4,6 +4,8 @@
 
 * A `webR.version` property has been added, containing the current version and build information (#409).
 
+* An `RObject.class()` method has been added, returning an `RCharacter` object with the names of the classes from which the given R object inherits. This has been implemented using R's `class()` function, and so the implicit class is similarly returned when the R object has no `class` attribute.
+
 # webR 0.3.2
 
 ## New features

src/tests/webR/robj.test.ts

@@ -53,6 +53,40 @@ test('Get RObject type as a string', async () => {
   expect(await result.toString()).toEqual('[object RObject:null]');
 });
 
+describe('Working with R object classes', () => {
+  test('Get R object intrinsic class', async () => {
+    const numeric = await new webR.RDouble([1, 2, 3]);
+    const character = await new webR.RCharacter(['a', 'b', 'c']);
+
+    const numericClass = await numeric.class();
+    const characterClass = await character.class();
+    expect(await numericClass.toArray()).toContain("numeric");
+    expect(await characterClass.toArray()).toContain("character");
+  });
+
+  test('Get R object class vector', async () => {
+    const jsObj = { a: [1, 2, 3], b: [3, 4, 5], c: ['x', 'y', 'z'] };
+    const rObj = await new webR.RDataFrame(jsObj);
+    const classes = await rObj.class();
+    expect(await classes.toArray()).toEqual(["data.frame"]);
+  });
+
+  test('Get R object class vector from attributes', async () => {
+    const rObj = await webR.evalR('x <- 123; class(x) <- c("abc", "def"); x');
+    const classes = await rObj.class();
+    expect(await classes.toArray()).toEqual(["abc", "def"]);
+  });
+
+  test('Get S4 R object class vector', async () => {
+    const rClass = await webR.evalR('getClass("MethodDefinition")');
+    const classes = await rClass.class();
+    const attrs = await rClass.attrs();
+    const attrPackage = await attrs.get('package');
+    expect(await classes.toArray()).toEqual(["classRepresentation"]);
+    expect(await attrPackage.toString()).toEqual("methods");
+  });
+});
+
 describe('Working with R lists and vectors', () => {
   test('Get R object attributes', async () => {
     const vector = await webR.evalR('c(a=1, b=2, c=3)');

src/webR/robj-worker.ts

@@ -243,6 +243,17 @@ export class RObject extends RObjectBase {
     return RPairlist.wrap(Module._ATTRIB(this.ptr));
   }
 
+  class(): RCharacter {
+    const prot = { n: 0 };
+    const classCall = new RCall([new RSymbol('class'), this]);
+    protectInc(classCall, prot);
+    try {
+      return classCall.eval() as RCharacter;
+    } finally {
+      unprotect(prot.n);
+    }
+  }
+
   setNames(values: (string | null)[] | null): this {
     let namesObj: RObject;