Add explicit conversion to bool in ThreadSafeFunctor

[jdv85]

In my project, when trying to check if an choc::threading::ThreadSafeFunctor<std::function<void()>> instance holds a value, I get this compiler error:

choc/threading/choc_ThreadSafeFunctor.h:142:12: error: no viable conversion from returned value of type 'std::function<void ()>' to function return type 'bool'
    return callback->fn;
           ^~~~~~~~~~~~

The problem seems to be that std::function marks it conversion to bool as explicit. I can fix the problem by using an explicit conversion in choc:

diff --git a/threading/choc_ThreadSafeFunctor.h b/threading/choc_ThreadSafeFunctor.h
index f58e5d8..2f02f1d 100644
--- a/threading/choc_ThreadSafeFunctor.h
+++ b/threading/choc_ThreadSafeFunctor.h
@@ -139,7 +139,7 @@ template <typename FunctionType>
 ThreadSafeFunctor<FunctionType>::operator bool() const
 {
     std::scoped_lock l (callback->lock);
-    return callback->fn;
+    return (bool)callback->fn;
 }
 
 template <typename FunctionType>

I'm not sure this is the best fix, but it works for me.

Here's a test case that illustrates the use case:

diff --git a/tests/choc_tests.h b/tests/choc_tests.h
index 1dfed39..919d3e6 100644
--- a/tests/choc_tests.h
+++ b/tests/choc_tests.h
@@ -2870,6 +2870,18 @@ inline void testThreading (choc::test::TestProgress& progress)
     {
         CHOC_TEST (ThreadSafeFunctor)
 
+        {
+            choc::threading::ThreadSafeFunctor<std::function<void()>> tsf;
+
+            CHOC_EXPECT_FALSE (tsf);
+            tsf = [] () {  };
+            CHOC_EXPECT_TRUE (tsf);
+
+            tsf.reset();
+            CHOC_EXPECT_FALSE (tsf);
+        }
+
+
         {
             choc::threading::ThreadSafeFunctor<std::function<void(int)>> tsf;

I'm building with Clang from Xcode 15.4.