From db608c8eb1a6b0ca3156f77732b1a66c923a1435 Mon Sep 17 00:00:00 2001
From: trivernis <trivernis@protonmail.com>
Date: Sun, 13 Mar 2022 20:37:57 +0100
Subject: [PATCH] Change register_traits to create_object to not associate
 wrong v-tables

Signed-off-by: trivernis <trivernis@protonmail.com>
---
 Cargo.toml    |  2 +-
 src/lib.rs    | 12 ++++++++++--
 src/macros.rs | 49 ++++++++++++++++++++++++++++++-------------------
 src/tests.rs  |  4 +++-
 4 files changed, 44 insertions(+), 23 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index 052d03a..c6d76cb 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "multi-trait-object"
-version = "0.1.3"
+version = "0.2.0"
 edition = "2021"
 readme = "README.md"
 license = "Apache-2.0"
diff --git a/src/lib.rs b/src/lib.rs
index 908db16..9d55232 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -20,14 +20,21 @@ pub struct FatPointer {
     pub vptr: *const (),
 }
 
+#[allow(unused)]
+#[doc(hidden)]
+#[inline]
+pub unsafe fn null_ptr<T: Sized>(_value: &T) -> *const T {
+    // creates a typed clone that is actually null
+    std::ptr::null::<T>() as *const T
+}
+
 /// A container to store data with the associated type and trait objects
 /// allowing for casting down to trait_impl or the concrete type
 /// ```rust
 /// use multi_trait_object::*;
 /// use std::fmt::{Debug, Display};
 ///
-/// let mut mto = MultitraitObject::new(String::new());
-/// register_traits!(mto, String, dyn Debug, dyn Display);
+/// let mto = create_object!(String::new(), dyn Debug, dyn Display);
 ///
 /// let debug = mto.downcast_trait::<dyn Debug>().unwrap();
 /// println!("{:?}", debug);
@@ -46,6 +53,7 @@ impl MultitraitObject {
     /// Creates a new multitrait object from the given value
     /// All trait_impl except Any must be registered on this object
     /// in order to access them.
+    #[doc(hidden)]
     pub fn new<T: 'static + Any>(value: T) -> Self {
         let any_vtable = __fat_pointer!(T as dyn Any).vptr;
         let data = Box::into_raw(Box::new(value)) as *mut ();
diff --git a/src/macros.rs b/src/macros.rs
index 1e1a62d..854e07b 100644
--- a/src/macros.rs
+++ b/src/macros.rs
@@ -20,7 +20,7 @@ macro_rules! impl_trait_object {
             fn into_multitrait(self) -> $crate::MultitraitObject {
                 let mut mto = $crate::MultitraitObject::new(self);
                 $(
-                    $crate::register_traits!(mto, $obj, $trt);
+                    mto._register::<$trt>($crate::__fat_pointer!($obj as $trt).vptr);
                 )*
 
                 mto
@@ -29,24 +29,6 @@ macro_rules! impl_trait_object {
     }
 }
 
-/// Registers multiple trait_impl on a multitrait object
-/// ```rust
-/// use multi_trait_object::*;
-/// use std::fmt::{Debug, Display};
-///
-/// let value = String::new();
-/// let mut mto = MultitraitObject::new(value);
-/// register_traits!(mto, String, dyn Debug, dyn Display);
-/// ```
-#[macro_export]
-macro_rules! register_traits {
-    ($r:expr, $v:ty, $($t:ty), +) => {
-        $(
-            $r._register::<$t>($crate::__fat_pointer!($v as $t).vptr);
-        )+
-    }
-}
-
 #[doc(hidden)]
 #[macro_export]
 macro_rules! __fat_pointer {
@@ -58,3 +40,32 @@ macro_rules! __fat_pointer {
         }
     }}
 }
+
+/// Registers multiple trait_impl on a multitrait object
+/// ```rust
+/// use multi_trait_object::*;
+/// use std::fmt::{Debug, Display};
+///
+/// let mto = create_object!(String::new(), dyn Debug, dyn Display);
+/// ```
+#[macro_export]
+macro_rules! create_object {
+    ($v:expr, $($t:ty), +) => {
+        {
+            let null_ptr = unsafe {
+                // SAFETY: We're never accessing the null value
+                $crate::null_ptr(&$v)
+            };
+            let mut mto = $crate::MultitraitObject::new($v);
+            $(
+                let vptr = unsafe {
+                    // SAFETY: We're never accessing the null value
+                    let ptr = $crate::null_ptr(&*null_ptr) as *const $t;
+                    std::mem::transmute::<_, $crate::FatPointer>(ptr).vptr
+                };
+                mto._register::<$t>(vptr);
+            )+
+            mto
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/tests.rs b/src/tests.rs
index 94d9e1f..32015f5 100644
--- a/src/tests.rs
+++ b/src/tests.rs
@@ -1,5 +1,5 @@
 use std::fmt::Debug;
-use crate::{__fat_pointer, impl_trait_object, IntoMultitrait, TryClone, TryPartialEq, RawClone, PartialEqAny};
+use crate::{__fat_pointer, impl_trait_object, IntoMultitrait, TryClone, TryPartialEq, RawClone, PartialEqAny, create_object};
 
 #[derive(Clone, Debug, Eq, PartialEq)]
 struct TestStruct {
@@ -42,6 +42,8 @@ fn it_creates_fat_pointers() {
 fn it_constructs() {
     TestStruct::default().into_multitrait();
     String::from("test").into_multitrait();
+    let mto = create_object!(String::from("test"), dyn Debug);
+    assert!(mto.is::<String>())
 }
 
 #[test]