From fff906a78ba545e77d087a82711b30bcc8e0d0c5 Mon Sep 17 00:00:00 2001
From: Matthias Schiffer <mschiffer@universe-factory.net>
Date: Sun, 5 Apr 2020 14:22:59 +0200
Subject: Introduce SafePtr trait, cleanup

---
 safe_libc/src/boxed.rs | 104 +++++++++++++++++++------------------------------
 src/main.rs            |  31 +++++++++------
 2 files changed, 60 insertions(+), 75 deletions(-)

diff --git a/safe_libc/src/boxed.rs b/safe_libc/src/boxed.rs
index 625c5b0..fa3e45d 100644
--- a/safe_libc/src/boxed.rs
+++ b/safe_libc/src/boxed.rs
@@ -26,11 +26,40 @@ fn slice_len<T>(p: *const [T]) -> usize {
 	unsafe { mem::transmute::<_, [usize; 2]>(p)[1] }
 }
 
-pub struct CBox<T: ?Sized>(*mut T);
+pub trait SafePtr {
+	fn safe_ptr(p: *mut Self) -> *mut Self;
+}
+
+impl<T> SafePtr for T {
+	#[inline]
+	fn safe_ptr(p: *mut T) -> *mut T {
+		if util::zst::<T>(1) {
+			return dangling();
+		}
+
+		debug_assert!(!p.is_null(), "NULL ptr");
+		p
+	}
+}
+
+impl<T> SafePtr for [T] {
+	#[inline]
+	fn safe_ptr(p: *mut [T]) -> *mut [T] {
+		let len = slice_len(p);
+		if util::zst::<T>(len) {
+			return ptr::slice_from_raw_parts_mut(dangling(), len);
+		}
 
-impl<T: ?Sized> CBox<T> {
+		debug_assert!(!p.is_null(), "NULL ptr");
+		p
+	}
+}
+
+pub struct CBox<T: SafePtr + ?Sized>(*mut T);
+
+impl<T: SafePtr + ?Sized> CBox<T> {
 	#[inline]
-	pub const unsafe fn from_raw_unchecked(p: *mut T) -> CBox<T> {
+	pub unsafe fn from_raw_unchecked(p: *mut T) -> CBox<T> {
 		CBox(p)
 	}
 
@@ -42,7 +71,7 @@ impl<T: ?Sized> CBox<T> {
 	}
 
 	#[inline]
-	pub const fn as_ptr(&self) -> *const T {
+	pub fn as_ptr(&self) -> *const T {
 		self.0
 	}
 
@@ -78,32 +107,9 @@ impl<T> CBox<T> {
 		util::check_ptr(p, len);
 		CBox::slice_from_raw_parts_unchecked(p, len)
 	}
-
-	#[inline]
-	fn safe_ptr(&self) -> *mut T {
-		if util::zst::<T>(1) {
-			return dangling();
-		}
-
-		debug_assert!(!self.0.is_null(), "NULL ptr");
-		self.0
-	}
-}
-
-impl<T> CBox<[T]> {
-	#[inline]
-	fn safe_ptr(&self) -> *mut [T] {
-		if self.0.is_null() {
-			let len = slice_len(self.0);
-			debug_assert!(util::zst::<T>(len), "NULL ptr");
-			return ptr::slice_from_raw_parts_mut(dangling(), len);
-		}
-
-		self.0
-	}
 }
 
-impl<T: ?Sized> Drop for CBox<T> {
+impl<T: SafePtr + ?Sized> Drop for CBox<T> {
 	#[inline]
 	fn drop(&mut self) {
 		unsafe {
@@ -113,60 +119,30 @@ impl<T: ?Sized> Drop for CBox<T> {
 	}
 }
 
-impl<T> Deref for CBox<T> {
+impl<T: SafePtr + ?Sized> Deref for CBox<T> {
 	type Target = T;
 
 	#[inline]
 	fn deref(&self) -> &T {
-		unsafe { &*self.safe_ptr() }
+		unsafe { &*T::safe_ptr(self.0) }
 	}
 }
 
-impl<T> DerefMut for CBox<T> {
+impl<T: SafePtr + ?Sized> DerefMut for CBox<T> {
 	#[inline]
 	fn deref_mut(&mut self) -> &mut T {
-		unsafe { &mut *self.safe_ptr() }
-	}
-}
-
-impl<T> Deref for CBox<[T]> {
-	type Target = [T];
-
-	#[inline]
-	fn deref(&self) -> &[T] {
-		unsafe { &*self.safe_ptr() }
-	}
-}
-
-impl<T> DerefMut for CBox<[T]> {
-	#[inline]
-	fn deref_mut(&mut self) -> &mut [T] {
-		unsafe { &mut *self.safe_ptr() }
-	}
-}
-
-impl<T: fmt::Debug> fmt::Debug for CBox<T> {
-	#[inline]
-	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-		fmt::Debug::fmt(&**self, f)
+		unsafe { &mut *T::safe_ptr(self.0) }
 	}
 }
 
-impl<T> fmt::Debug for CBox<[T]> where [T]: fmt::Debug {
+impl<T: fmt::Debug + SafePtr + ?Sized> fmt::Debug for CBox<T> {
 	#[inline]
 	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 		fmt::Debug::fmt(&**self, f)
 	}
 }
 
-impl<T: fmt::Display> fmt::Display for CBox<T> {
-	#[inline]
-	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-		fmt::Display::fmt(&**self, f)
-	}
-}
-
-impl<T> fmt::Display for CBox<[T]> where [T]: fmt::Display {
+impl<T: fmt::Display + SafePtr + ?Sized> fmt::Display for CBox<T> {
 	#[inline]
 	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 		fmt::Display::fmt(&**self, f)
diff --git a/src/main.rs b/src/main.rs
index 944b7ab..c79f1da 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -9,17 +9,26 @@ use core::fmt::Write;
 #[no_mangle]
 pub extern "C" fn main(_nargs: libc::c_int, _args: *const *const libc::c_char) -> libc::c_int {
 	let mut stdout = unsafe { libc::stdio::stdout() };
-	let x = libc::string::CString::from("foo");
-	let l = x.len();
-	let y = x.into_raw();
-	let z = unsafe {
-		libc::boxed::CBox::slice_from_raw_parts(y, l)
-	};
-	let foo = cstr!("Foo!\n");
-	stdout.puts(foo);
-	let _ = writeln!(stdout, "Foo: {} {} {}", z[0], z[1], z[2]);
-	let b = libc::boxed::CBox::new(42);
-	let _ = writeln!(stdout, "Bar: {}", b);
+
+	{
+		let foo = cstr!("Foo!\n");
+		stdout.puts(foo);
+	}
+
+	{
+		let x = libc::string::CString::from("foo");
+		let l = x.len();
+		let y = x.into_raw();
+		let z = unsafe {
+			libc::boxed::CBox::slice_from_raw_parts(y, l)
+		};
+		let _ = writeln!(stdout, "Foo: {} {} {}", z[0], z[1], z[2]);
+	}
+
+	{
+		let b = libc::boxed::CBox::new(42);
+		let _ = writeln!(stdout, "Bar: {}", b);
+	}
 	0
 }
 
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