1 files changed, 42 insertions, 0 deletions
diff --git a/compat/borrowed-ptr-cast.hpp b/compat/borrowed-ptr-cast.hpp
new file mode 100644
index 00000000..b9db2e5b
--- /dev/null
+++ b/compat/borrowed-ptr-cast.hpp
@@ -0,0 +1,42 @@
+#pragma once
+#include "borrowed-ptr-fwd.hpp"
+#include "compat/assert.hpp"
+
+namespace floormat::detail_borrowed_ptr {
+
+//static_assert(std::is_same_v<T, U> || std::has_virtual_destructor_v<T> && std::has_virtual_destructor_v<T>); // todo! for simple_bptr
+
+template<typename From, typename To>
+concept StaticCastable = requires(From* from) {
+    static_cast<To*>(from);
+};
+
+} // namespace floormat::detail_borrowed_ptr
+
+namespace floormat {
+
+template<typename To, typename From>
+bptr<To> static_pointer_cast(const bptr<From>& p) noexcept
+{
+    // hack to generate better error message
+    if constexpr (detail_borrowed_ptr::StaticCastable<From, To>)
+    {
+        if (p.blk && p.blk->_ptr) [[likely]]
+        {
+            fm_assert(p.casted_ptr);
+            auto* ret = static_cast<To*>(p.casted_ptr);
+            return bptr<To>{DirectInit, ret, p.blk};
+        }
+    }
+    else
+    {
+        using detail_borrowed_ptr::StaticCastable;
+        // concepts can't be forward-declared so use static_assert
+        static_assert(StaticCastable<From, To>,
+            "cannot static_cast, classes must be related by inheritance");
+    }
+
+    return bptr<To>{nullptr};
+}
+
+} // namespace floormat