From 33ed570ac445d379530c3e55de240508cd4d71fe Mon Sep 17 00:00:00 2001
From: Shawn Silverman <shawn@pobox.com>
Date: Fri, 1 Sep 2023 19:05:31 -0700
Subject: [PATCH] Fix compile error for non-void-returning inplace_functions

The error occurs when testing for or calling an unassigned function.
---
 teensy3/inplace_function.h | 15 +++++++++------
 teensy4/inplace_function.h | 15 +++++++++------
 2 files changed, 18 insertions(+), 12 deletions(-)

diff --git a/teensy3/inplace_function.h b/teensy3/inplace_function.h
index 0d716d1a..fbc99d1d 100644
--- a/teensy3/inplace_function.h
+++ b/teensy3/inplace_function.h
@@ -1,9 +1,4 @@
-#pragma once
-
 // https://github.com/WG21-SG14/SG14/blob/master/SG14/inplace_function.h
-//
-// For use with Teensy, allow uninitialized to be no-operation without error
-#define SG14_INPLACE_FUNCTION_THROW(x)
 
 /*
  * Boost Software License - Version 1.0 - August 17th, 2003
@@ -31,13 +26,21 @@
  * DEALINGS IN THE SOFTWARE.
  */
 
+#pragma once
+
 #include <type_traits>
 #include <utility>
 #include <functional>
 #include <cstddef>
 
+// Teensy doesn't support runtime exceptions, so calling an uninitialized
+// inplace_function needs to call a non-returning function. We can't do nothing
+// because that would cause a compile error for non-void-returning functions.
+// Additionally, we can't return some default value because that's not possible
+// for return types that have a non-trivial constructor.
+// See 'invoke_ptr' initialization in 'vtable()' constructor.
 #ifndef SG14_INPLACE_FUNCTION_THROW
-#define SG14_INPLACE_FUNCTION_THROW(x) throw (x)
+#define SG14_INPLACE_FUNCTION_THROW(x) std::__throw_bad_function_call()
 #endif
 
 namespace stdext {
diff --git a/teensy4/inplace_function.h b/teensy4/inplace_function.h
index 0d716d1a..fbc99d1d 100644
--- a/teensy4/inplace_function.h
+++ b/teensy4/inplace_function.h
@@ -1,9 +1,4 @@
-#pragma once
-
 // https://github.com/WG21-SG14/SG14/blob/master/SG14/inplace_function.h
-//
-// For use with Teensy, allow uninitialized to be no-operation without error
-#define SG14_INPLACE_FUNCTION_THROW(x)
 
 /*
  * Boost Software License - Version 1.0 - August 17th, 2003
@@ -31,13 +26,21 @@
  * DEALINGS IN THE SOFTWARE.
  */
 
+#pragma once
+
 #include <type_traits>
 #include <utility>
 #include <functional>
 #include <cstddef>
 
+// Teensy doesn't support runtime exceptions, so calling an uninitialized
+// inplace_function needs to call a non-returning function. We can't do nothing
+// because that would cause a compile error for non-void-returning functions.
+// Additionally, we can't return some default value because that's not possible
+// for return types that have a non-trivial constructor.
+// See 'invoke_ptr' initialization in 'vtable()' constructor.
 #ifndef SG14_INPLACE_FUNCTION_THROW
-#define SG14_INPLACE_FUNCTION_THROW(x) throw (x)
+#define SG14_INPLACE_FUNCTION_THROW(x) std::__throw_bad_function_call()
 #endif
 
 namespace stdext {