Handle inherited fields correctly.

test/inheritance/inherit_fields.wren

@@ -0,0 +1,35 @@
+class Foo {
+  foo(a, b) {
+    _field1 = a
+    _field2 = b
+  }
+
+  fooPrint {
+    io.write(_field1)
+    io.write(_field2)
+  }
+}
+
+class Bar is Foo {
+  bar(a, b) {
+    _field1 = a
+    _field2 = b
+  }
+
+  barPrint {
+    io.write(_field1)
+    io.write(_field2)
+  }
+}
+
+var bar = Bar.new
+bar.foo("foo 1", "foo 2")
+bar.bar("bar 1", "bar 2")
+
+bar.fooPrint
+// expect: foo 1
+// expect: foo 2
+
+bar.barPrint
+// expect: bar 1
+// expect: bar 2

test/inheritance/inherit_methods.wren

@@ -0,0 +1,27 @@
+class Foo {
+  methodOnFoo { io.write("foo") }
+  method(a) { io.write("foo") }
+  method(a, b, c) { io.write("foo") }
+}
+
+class Bar is Foo {
+  methodOnBar { io.write("bar") }
+  method(a, b) { io.write("bar") }
+  method(a, b, c, d) { io.write("bar") }
+}
+
+var bar = Bar.new
+bar.methodOnFoo // expect: foo
+bar.methodOnBar // expect: bar
+
+// Methods with different arity do not shadow each other.
+bar.method(1) // expect: foo
+bar.method(1, 2) // expect: bar
+bar.method(1, 2, 3) // expect: foo
+bar.method(1, 2, 3, 4) // expect: bar
+
+// TODO(bob): Overriding (or BETA-style refining?).
+// TODO(bob): Private fields.
+// TODO(bob): Super (or inner) calls.
+// TODO(bob): Grammar for what expressions can follow "is".
+// TODO(bob): Prevent extending built-in types.

test/inheritance/is.wren

@@ -0,0 +1,16 @@
+class A {}
+class B is A {}
+class C is B {}
+var a = A.new
+var b = B.new
+var c = C.new
+
+io.write(a is A) // expect: true
+io.write(a is B) // expect: false
+io.write(a is C) // expect: false
+io.write(b is A) // expect: true
+io.write(b is B) // expect: true
+io.write(b is C) // expect: false
+io.write(c is A) // expect: true
+io.write(c is B) // expect: true
+io.write(c is C) // expect: true