From 5c54707ed13c2996f36b99dddb76f017765cec72 Mon Sep 17 00:00:00 2001
From: Stanislaw Halik <sthalik@misaki.pl>
Date: Sat, 4 May 2024 20:13:15 +0200
Subject: a w

---
 compat/borrowed-ptr-fwd.hpp |  2 +-
 compat/borrowed-ptr.hpp     | 13 ++++++++-----
 2 files changed, 9 insertions(+), 6 deletions(-)

(limited to 'compat')

diff --git a/compat/borrowed-ptr-fwd.hpp b/compat/borrowed-ptr-fwd.hpp
index da91502d..465e9bf4 100644
--- a/compat/borrowed-ptr-fwd.hpp
+++ b/compat/borrowed-ptr-fwd.hpp
@@ -44,7 +44,7 @@ public:
     T& operator*() const noexcept;
 
     template<typename U> friend class bptr;
-    template<typename Tʹ, typename U> friend bptr<U> static_pointer_cast(const bptr<Tʹ>& p) noexcept;
+    template<typename U, typename Tʹ> friend bptr<U> static_pointer_cast(const bptr<Tʹ>& p) noexcept;
 };
 
 } // namespace floormat
diff --git a/compat/borrowed-ptr.hpp b/compat/borrowed-ptr.hpp
index 5caa2261..d13d8ee2 100644
--- a/compat/borrowed-ptr.hpp
+++ b/compat/borrowed-ptr.hpp
@@ -28,20 +28,23 @@ concept StaticCastable = requires(From* from) {
 
 namespace floormat {
 
-template<typename T, typename U>
+template<typename U, typename T>
 bptr<U> static_pointer_cast(const bptr<T>& p) noexcept
 {
-    static_assert(detail_borrowed_ptr::StaticCastable<T, U>);
-
-    if (p.blk) [[likely]]
+    // hack to generate better error message
+    if constexpr (detail_borrowed_ptr::StaticCastable<T, U>)
     {
-        if (auto* ptr = p.blk->_ptr)
+        if (p.blk && p.blk->_ptr) [[likely]]
         {
             fm_bptr_assert(p.casted_ptr);
             auto* ret = static_cast<U*>(p.casted_ptr);
             return bptr<U>{DirectInit, ret, p.blk};
         }
     }
+    else
+        // concepts can't be forward-declared so use static_assert
+        static_assert(detail_borrowed_ptr::StaticCastable<T, U>);
+
     return bptr<U>{nullptr};
 }
 
-- 
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