From 24cee49f6d6fcd9f9755a50f32d56fb733c462ab Mon Sep 17 00:00:00 2001
From: Antony Chan <antony.sigma@gmail.com>
Date: Thu, 20 Jul 2023 10:18:01 -0700
Subject: [PATCH] Constrain the Property object at compile-time

The property struct/class requires a public member function signature
`apply(hid_t) const`. Describe the constrain in the C++20 concepts
syntax. The primarily goal is to make compiler errors more readable for
average users. Average users are those who do not understand SFINAE.
---
 include/highfive/H5PropertyList.hpp           | 25 +++++++++++++++++--
 include/highfive/bits/H5PropertyList_misc.hpp |  2 +-
 2 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/include/highfive/H5PropertyList.hpp b/include/highfive/H5PropertyList.hpp
index db541a42f..af149a94a 100644
--- a/include/highfive/H5PropertyList.hpp
+++ b/include/highfive/H5PropertyList.hpp
@@ -133,6 +133,27 @@ class PropertyListBase: public Object {
     friend T details::get_plist(const U&, hid_t (*f)(hid_t));
 };
 
+/// \interface PropertyInterface
+/// \brief HDF5 file property object
+///
+/// A property is an object which is expected to have a method with the
+/// following signature `void apply(hid_t hid) const`
+///
+/// \sa Instructions to document C++20 concepts with Doxygen: https://github.com/doxygen/doxygen/issues/2732#issuecomment-509629967
+///
+/// \cond
+#if __cplusplus >= 202002L
+template<typename P>
+concept PropertyInterface = requires(P p, const hid_t hid)
+{
+    { p.apply(hid) };
+};
+
+#else
+#define PropertyInterface typename
+#endif
+/// \endcond
+
 ///
 /// \brief HDF5 property Lists
 ///
@@ -149,8 +170,8 @@ class PropertyList: public PropertyListBase {
     /// Add a property to this property list.
     /// A property is an object which is expected to have a method with the
     /// following signature void apply(hid_t hid) const
-    ///
-    template <typename P>
+    /// \tparam PropertyInterface
+    template <PropertyInterface P>
     void add(const P& property);
 
     ///
diff --git a/include/highfive/bits/H5PropertyList_misc.hpp b/include/highfive/bits/H5PropertyList_misc.hpp
index cf94af832..cef301e53 100644
--- a/include/highfive/bits/H5PropertyList_misc.hpp
+++ b/include/highfive/bits/H5PropertyList_misc.hpp
@@ -70,7 +70,7 @@ inline void PropertyList<T>::_initializeIfNeeded() {
 }
 
 template <PropertyType T>
-template <typename P>
+template <PropertyInterface P>
 inline void PropertyList<T>::add(const P& property) {
     _initializeIfNeeded();
     property.apply(_hid);