initial commit

.gitignore

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+/target
+Cargo.lock
+*~

Cargo.toml

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+[package]
+name = "phantomdrop"
+version = "0.1.0"
+authors = ["Avril <flanchan@cumallover.me>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

src/lib.rs

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+//! Small library for `defer`ing the running of function until the end of a block.
+
+use core::mem::MaybeUninit;
+use core::ops::Drop;
+
+/// When dropped, the included function is ran with the argument held by the structure.
+#[derive(Debug)]
+pub struct PhantomDrop<T, F: FnOnce(T)>(MaybeUninit<(T, F)>);
+
+impl<T: Clone, F: Clone + FnOnce(T)> Clone for PhantomDrop<T,F>
+{
+    #[inline] fn clone(&self) -> Self
+    {
+	let re = unsafe { self.value_ref() };
+	Self(MaybeUninit::new((re.0.clone(), re.1.clone())))
+    }
+}
+
+impl<F> PhantomDrop<(),F>
+where F: FnOnce(())
+{
+    /// Defer a function to run when this guard is dropped.
+    #[inline] pub fn defer(fun: F) -> Self
+    {
+	PhantomDrop::new((), fun)
+    }
+}
+impl<T, F> PhantomDrop<T,F>
+where F: FnOnce(T)
+{
+    #[inline(always)] unsafe fn value_mut(&mut self) -> &mut (T, F)
+    {
+	&mut (*self.0.as_mut_ptr())
+    }
+    #[inline(always)] unsafe fn value_ref(&self) -> &(T, F)
+    {
+	&(*self.0.as_ptr())
+    }
+    #[inline(always)] unsafe fn into_raw_parts(self) -> (T, F)
+    {
+	let (v, f) = self.0.as_ptr().read();
+	core::mem::forget(self);
+	(v, f)
+    }
+    
+    /// Defer a function to run on this stored value when this guard is 
+    #[inline] pub fn new(value: T, fun: F) -> Self
+    {
+	Self(MaybeUninit::new((value, fun)))
+    }
+
+    /// Consume the instance into its held type without running the drop closure.
+    #[inline] pub fn into_inner(self) -> T
+    {
+	unsafe { self.into_raw_parts() }.0
+    }
+
+    /// Get a mutable reference to the held type.
+    #[inline] pub fn as_mut(&mut self) -> &mut T
+    {
+	unsafe { &mut self.value_mut().0 }
+    }
+    /// Get a reference to the held type.
+    #[inline] pub fn as_ref(&self) -> &T
+    {
+	unsafe { &self.value_ref().0 }
+    }
+
+    /// Replace the function to be ran on drop with a no-op.
+    #[inline] pub fn neutralise(self) -> PhantomDrop<T, fn (T)>
+    {
+	PhantomDrop::new(self.into_inner(), drop)
+    }
+
+}
+
+impl<T: 'static> PhantomDrop<T, Box<dyn FnOnce(T)>>
+{
+    /// Box the closure in this instance.
+    #[inline] pub fn boxed(self) -> PhantomDrop<T, Box<dyn FnOnce(T)>>
+    {	
+	let (v, f) = unsafe { self.into_raw_parts() };
+	PhantomDrop::new(v, Box::new(f))
+    }
+
+    /// Replace the function to be ran on drop with a no-op in place.
+    #[inline] pub fn neutralise_boxed(&mut self)
+    {
+	unsafe { self.value_mut().1 = Box::new(drop) };
+    }
+}
+impl<T> PhantomDrop<T, fn (T)>
+{
+    /// Replace the function to be ran on drop with a no-op in place.
+    #[inline] pub fn neutralise_in_place(&mut self)
+    {
+	unsafe { self.value_mut().1 = drop };
+    }
+}
+
+
+impl<T, F> Drop for PhantomDrop<T,F>
+where F: FnOnce(T)
+{
+    #[inline] fn drop(&mut self)
+    {
+	let (v, f) = unsafe { self.0.as_ptr().read() };
+	f(v);
+    }
+}