Remove BindStateHolder and have Bind() return a Callback<> object directly.

base/bind_unittest.cc

Index: base/bind_unittest.cc
diff --git a/base/bind_unittest.cc b/base/bind_unittest.cc
index 654a2775a2f23efc2f266d8db8286e20fed15b0a..1eed9f7ee6a5416d7ad40d3ff10cb559949a353a 100644
--- a/base/bind_unittest.cc
+++ b/base/bind_unittest.cc
@@ -199,10 +199,18 @@ void RefArgSet(int &n) {
   n = 2;
 }
 
+void PtrArgSet(int *n) {
+  *n = 2;
+}
+
 int FunctionWithWeakFirstParam(WeakPtr<NoRef> o, int n) {
   return n;
 }
 
+void TakesACallback(const Closure& callback) {
+  callback.Run();
+}
+
 class BindTest : public ::testing::Test {
  public:
   BindTest() {
@@ -284,6 +292,25 @@ TEST_F(BindTest, CurryingTest) {
   EXPECT_EQ(63, c0.Run());
 }
 
+// Test that curring the rvalue result of Bind() works correclty.

[akalin, 2011/12/02 18:54:45]

curring -> currying

Although don't you mean 'binding'?

[awong, 2011/12/06 00:21:12]

Not sure there's a distinction...

[akalin, 2011/12/06 17:57:57]

currying = changing a function '(A, B) -> C' to 'A -> (B -> C)'.

partial application (or binding) = taking a function '(A, B...) -> C' and a
value a of type A and returning a function '(B...) -> C'.

+//   - rvalue should be usable as argument to Bind().
+//   - multiple runs of resulting Callback remain valid.
+TEST_F(BindTest, CurryingRvalueResultOfBind) {
+  int n = 0;
+  Closure cb = base::Bind(&TakesACallback, base::Bind(&PtrArgSet, &n));
+
+  // If we implemt Bind() such that the return value has auto_ptr-like

[akalin, 2011/12/02 18:54:45]

implemt -> implement

[awong, 2011/12/06 00:21:12]

Done.

+  // semantics, the second call here will fail because ownership of
+  // the internal BindState<> would have been trasnfered to a *temporary*

[akalin, 2011/12/02 18:54:45]

trasnfered -> transferred

[awong, 2011/12/06 00:21:12]

Done.

+  // constructon of a Callback object on the first call.
+  cb.Run();
+  EXPECT_EQ(2, n);
+
+  n = 0;
+  cb.Run();
+  EXPECT_EQ(2, n);
+}
+
 // Function type support.
 //   - Normal function.
 //   - Normal function bound with non-refcounted first argument.