From d3a4abe33670338c0a870a0e351697f43d2a385d Mon Sep 17 00:00:00 2001
From: Michael Pfaff <michael@pfaff.dev>
Date: Thu, 29 Jun 2023 00:37:23 -0400
Subject: [PATCH] Initial commit

---
 .gitignore |  2 ++
 Cargo.toml |  6 ++++++
 src/lib.rs | 17 +++++++++++++++++
 3 files changed, 25 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 Cargo.toml
 create mode 100644 src/lib.rs

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..96ef6c0
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+/target
+Cargo.lock
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..f70160e
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "typeid-cast"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..ccde957
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,17 @@
+use std::{any::TypeId, mem::ManuallyDrop};
+
+/// Safe cast using [`TypeId`].
+#[inline]
+pub fn cast<T: 'static, R: 'static>(t: T) -> Result<R, T> {
+    if TypeId::of::<T>() == TypeId::of::<R>() {
+        union U<T, R> {
+            t: ManuallyDrop<T>,
+            r: ManuallyDrop<R>,
+        }
+
+        // SAFETY: we've confirmed the types are the same.
+        Ok(unsafe { ManuallyDrop::into_inner(U { t: ManuallyDrop::new(t) }.r) })
+    } else {
+        Err(t)
+    }
+}