consume_ptr 0.3.0

#![feature(mem_copy_fn, box_into_inner)]
#![feature(const_trait_impl)]
#![feature(get_mut_unchecked)]
#![feature(new_uninit)]
#![feature(slice_ptr_len)]
#![feature(forget_unsized)]

use std::borrow::{BorrowMut, Cow};
use std::ffi::{CStr, CString, OsStr, OsString};
use std::marker::Destruct;
use std::mem::{ManuallyDrop, MaybeUninit, transmute};
use std::path::{Path, PathBuf};
use std::rc::Rc;
use std::sync::Arc;

/// this struct has memcpy on clone(), however it will be better to have wrapper that forces to Copy
/// that way it can handle unsized types better
#[repr(transparent)]
struct AlwaysCopy<T: ?Sized>(T);

impl<T: ?Sized + Sized> Clone for AlwaysCopy<T> {
    fn clone(&self) -> Self {
        unsafe {
            let mut ret = MaybeUninit::uninit().assume_init();
            std::intrinsics::copy_nonoverlapping(self, &mut ret as _, 1);
            ret
        }
    }
}
pub unsafe trait TryConsume<Target: ?Sized + ~const Destruct>: Sized {

    /// `Target` is never read after this call
    fn try_consume_unsized<T>(self, f: impl FnOnce(*mut Target) -> T) -> Result<T, Self>;

    fn try_consume(self) -> Result<Target, Self> where Target: Sized {
        unsafe {
            self.try_consume_unsized(|x| {
                let mut ret = MaybeUninit::uninit().assume_init();
                std::intrinsics::copy_nonoverlapping(x, &mut ret as _, 1);
                ret
            })
        }
    }

    fn try_into_owned(self) -> Result<<Target as ToOwned>::Owned, Self>
        where Target: ToOwned, <Target as ToOwned>::Owned: FromConsume<Target>
    {
        <Target as ToOwned>::Owned::try_from_consume(self)
    }
}

pub unsafe trait Consume<Target: ?Sized + ~const Destruct>: TryConsume<Target> {
    /// `Target` is never read after this call
    fn consume_unsized<T>(self, f: impl FnOnce(*mut Target) -> T) -> T;

    fn consume(self) -> Target where Target: Sized {
        unsafe {
            self.consume_unsized(|x| {
                let mut ret = MaybeUninit::uninit().assume_init();
                std::intrinsics::copy_nonoverlapping(x, &mut ret as _, 1);
                ret
            })
        }
    }

    fn into_owned(self) -> <Target as ToOwned>::Owned
        where Target: ToOwned, <Target as ToOwned>::Owned: FromConsume<Target>
    {
        <Target as ToOwned>::Owned::from_consume(self)
    }
}

unsafe impl<T> TryConsume<T> for T {
    fn try_consume_unsized<U>(self, f: impl FnOnce(*mut T) -> U) -> Result<U, Self> {
        Ok(self.consume_unsized(f))
    }
}

unsafe impl<T> Consume<T> for T {
    fn consume_unsized<U>(mut self, f: impl FnOnce(*mut T) -> U) -> U {
        let ret = f(&mut self as _);
        std::mem::forget_unsized(self);
        ret
    }
}

pub trait FromConsume<From: ?Sized>: Sized {
    unsafe fn from_consume_raw(p: *mut From) -> Self;

    fn try_from_consume<T: TryConsume<From>>(consume: T) -> Result<Self, T> {
        unsafe {
            consume.try_consume_unsized(|x| Self::from_consume_raw(x))
        }
    }

    fn from_consume<T: Consume<From> + TryConsume<From>>(consume: T) -> Self {
        unsafe {
            consume.consume_unsized(|x| Self::from_consume_raw(x))
        }
    }
}

macro_rules! unsized_copy {
    ($callback_macro:ident) => {
        $callback_macro!(str);
        $callback_macro!(CStr);
        $callback_macro!(OsStr);
        $callback_macro!(Path);
    };
}

impl<T> FromConsume<[T]> for Vec<T> {

    unsafe fn from_consume_raw(p: *mut [T]) -> Self {
        let ret = (p as *mut [AlwaysCopy<T>]).as_ref().unwrap_unchecked().to_vec();
        transmute(ret)
    }
}

unsafe impl<T> TryConsume<[T]> for Vec<T> where [T]: ToOwned<Owned=Vec<T>> {
    fn try_consume_unsized<U>(self, f: impl FnOnce(*mut [T]) -> U) -> Result<U, Self> {
        Ok(self.consume_unsized(f))
    }

    fn try_into_owned(self) -> Result<<[T] as ToOwned>::Owned, Self> {
        Ok(self)
    }
}

unsafe impl<T> Consume<[T]> for Vec<T> where [T]: ToOwned<Owned=Vec<T>> {
    fn consume_unsized<U>(mut self, f: impl FnOnce(*mut [T]) -> U) -> U {
        let ret = f(self.as_mut_slice() as _);
        unsafe { transmute::<_, Vec<ManuallyDrop<T>>>(self); }
        ret
    }

    fn into_owned(self) -> <[T] as ToOwned>::Owned {
        self
    }
}

impl FromConsume<str> for String {
    unsafe fn from_consume_raw(p: *mut str) -> Self {
        p.as_ref().unwrap_unchecked().to_string()
    }
}

unsafe impl TryConsume<str> for String {
    fn try_consume_unsized<T>(self, f: impl FnOnce(*mut str) -> T) -> Result<T, Self> {
        Ok(self.consume_unsized(f))
    }

    fn try_into_owned(self) -> Result<String, Self> {
        Ok(self)
    }
}

unsafe impl Consume<str> for String {
    fn consume_unsized<T>(mut self, f: impl FnOnce(*mut str) -> T) -> T {
        f(self.as_mut_str() as _)
    }
    fn into_owned(self) -> String {
        self
    }
}

impl FromConsume<CStr> for CString {
    unsafe fn from_consume_raw(p: *mut CStr) -> Self {
        p.as_ref().unwrap_unchecked().to_owned()
    }
}

unsafe impl TryConsume<CStr> for CString {
    fn try_consume_unsized<T>(self, f: impl FnOnce(*mut CStr) -> T) -> Result<T, Self> {
        Ok(self.consume_unsized(f))
    }

    fn try_into_owned(self) -> Result<CString, Self> {
        Ok(self)
    }
}

unsafe impl Consume<CStr> for CString {
    fn consume_unsized<T>(self, f: impl FnOnce(*mut CStr) -> T) -> T {
        f(self.as_c_str() as *const _ as *mut _)
    }
    fn into_owned(self) -> CString {
        self
    }
}

impl FromConsume<OsStr> for OsString {
    unsafe fn from_consume_raw(p: *mut OsStr) -> Self {
        p.as_ref().unwrap_unchecked().to_owned()
    }
}

unsafe impl TryConsume<OsStr> for OsString {
    fn try_consume_unsized<T>(self, f: impl FnOnce(*mut OsStr) -> T) -> Result<T, Self> {
        Ok(self.consume_unsized(f))
    }

    fn try_into_owned(self) -> Result<OsString, Self> {
        Ok(self)
    }
}

unsafe impl Consume<OsStr> for OsString {
    fn consume_unsized<T>(self, f: impl FnOnce(*mut OsStr) -> T) -> T {
        f(self.as_os_str() as *const _ as *mut _)
    }
    fn into_owned(self) -> OsString {
        self
    }
}

impl FromConsume<Path> for PathBuf {
    unsafe fn from_consume_raw(p: *mut Path) -> Self {
        p.as_ref().unwrap_unchecked().to_owned()
    }
}

unsafe impl TryConsume<Path> for PathBuf {
    fn try_consume_unsized<T>(self, f: impl FnOnce(*mut Path) -> T) -> Result<T, Self> {
        Ok(self.consume_unsized(f))
    }

    fn try_into_owned(self) -> Result<Self, Self> {
        Ok(self)
    }
}

unsafe impl Consume<Path> for PathBuf {
    fn consume_unsized<T>(self, f: impl FnOnce(*mut Path) -> T) -> T {
        f(self.as_path() as *const _ as *mut _)
    }
    fn into_owned(self) -> Self {
        self
    }
}

unsafe impl<T: ?Sized> TryConsume<T> for Box<T> {
    fn try_consume_unsized<U>(self, f: impl FnOnce(*mut T) -> U) -> Result<U, Self> {
        Ok(self.consume_unsized(f))
    }

    fn try_consume(self) -> Result<T, Self> where T: Sized {
        Ok(self.consume())
    }
}

unsafe impl<T: ?Sized> Consume<T> for Box<T> {
    fn consume_unsized<U>(mut self, f: impl FnOnce(*mut T) -> U) -> U {
        let ret = f(self.borrow_mut() as *mut T);
        unsafe { transmute::<_, Box<ManuallyDrop<T>>>(self); }
        ret
    }

    fn consume(self) -> T where T: Sized {
        Box::into_inner(self)
    }
}

impl<T> FromConsume<T> for Box<T> {
    unsafe fn from_consume_raw(p: *mut T) -> Self {
        let x = Box::from_raw(p as *mut AlwaysCopy<T>);
        let ret = x.clone();
        Box::leak(x);
        transmute(ret)
    }
}

impl<T> FromConsume<[T]> for Box<[T]> {
    unsafe fn from_consume_raw(p: *mut [T]) -> Self {
        let x = Box::from_raw(p as *mut [AlwaysCopy<T>]);
        let ret = x.clone();
        Box::leak(x);
        transmute(ret)
    }
}

macro_rules! box_unsized {
    ($t:ty) => {
        impl FromConsume<$t> for Box<$t> {
            unsafe fn from_consume_raw(p: *mut $t) -> Self {
                let x = Box::from_raw(p);
                let ret = x.clone();
                Box::leak(x);
                transmute(ret)
            }
        }
    };
}

unsized_copy!(box_unsized);

unsafe impl<T: ?Sized> TryConsume<T> for Arc<T> {
    fn try_consume_unsized<U>(mut self, f: impl FnOnce(*mut T) -> U) -> Result<U, Self> {
        if let Some(x) = Arc::get_mut(&mut self) {
            let ret = f(x as _);
            unsafe { transmute::<_, Arc<ManuallyDrop<T>>>(self); }
            Ok(ret)
        } else {
            Err(self)
        }
    }
}

impl<T> FromConsume<T> for Arc<T> {

    unsafe fn from_consume_raw(p: *mut T) -> Self {
        let x = Box::from_raw(p as *mut AlwaysCopy<T>);
        let mut ret: Arc<MaybeUninit<AlwaysCopy<T>>> = Arc::new_uninit();
        std::intrinsics::copy_nonoverlapping(p as *const AlwaysCopy<T>, Arc::get_mut_unchecked(&mut ret).assume_init_mut() as *mut AlwaysCopy<T>, 1);
        Box::leak(x);
        transmute(ret.assume_init())
    }
}

impl<T> FromConsume<[T]> for Arc<[T]> {

    unsafe fn from_consume_raw(p: *mut [T]) -> Self {
        let x = Box::from_raw(p as *mut [AlwaysCopy<T>]);
        let mut ret: Arc<[MaybeUninit<AlwaysCopy<T>>]> = Arc::new_uninit_slice(p.len());
        std::intrinsics::copy_nonoverlapping(p as *const AlwaysCopy<T>, Arc::get_mut_unchecked(&mut ret).as_mut_ptr() as *mut AlwaysCopy<T>, p.len());
        Box::leak(x);
        transmute(ret.assume_init())
    }
}

macro_rules! arc_unsized {
    ($t:ty) => {
        impl FromConsume<$t> for Arc<$t> {

            unsafe fn from_consume_raw(p: *mut $t) -> Self {
                let x = Box::from_raw(p);
                let ret = (&*x).into();
                Box::leak(x);
                ret
            }
        }
    };
}

unsized_copy!(arc_unsized);

unsafe impl<T: ?Sized> TryConsume<T> for Rc<T> {
    fn try_consume_unsized<U>(mut self, f: impl FnOnce(*mut T) -> U) -> Result<U, Self> {
        if let Some(x) = Rc::get_mut(&mut self) {
            let ret = f(x as _);
            unsafe { transmute::<_, Rc<ManuallyDrop<T>>>(self); }
            Ok(ret)
        } else {
            Err(self)
        }
    }
}

impl<T> FromConsume<T> for Rc<T> {
    unsafe fn from_consume_raw(p: *mut T) -> Self {
        let x = Box::from_raw(p as *mut AlwaysCopy<T>);
        let mut ret: Rc<MaybeUninit<AlwaysCopy<T>>> = Rc::new_uninit();
        std::intrinsics::copy_nonoverlapping(p as *const AlwaysCopy<T>, Rc::get_mut_unchecked(&mut ret).assume_init_mut() as *mut AlwaysCopy<T>, 1);
        Box::leak(x);
        transmute(ret.assume_init())
    }
}

impl<T> FromConsume<[T]> for Rc<[T]> {

    unsafe fn from_consume_raw(p: *mut [T]) -> Self {
        let x = Box::from_raw(p as *mut [AlwaysCopy<T>]);
        let mut ret: Rc<[MaybeUninit<AlwaysCopy<T>>]> = Rc::new_uninit_slice(p.len());
        std::intrinsics::copy_nonoverlapping(p as *const AlwaysCopy<T>, Rc::get_mut_unchecked(&mut ret).as_mut_ptr() as *mut AlwaysCopy<T>, p.len());
        Box::leak(x);
        transmute(ret.assume_init())
    }
}

macro_rules! rc_unsized {
    ($t:ty) => {
        impl FromConsume<$t> for Rc<$t> {
            unsafe fn from_consume_raw(p: *mut $t) -> Self {
                let x = Box::from_raw(p);
                let ret = (&*x).into();
                Box::leak(x);
                ret
            }
        }
    };
}

unsized_copy!(rc_unsized);

unsafe impl<T: ToOwned + ?Sized> TryConsume<T> for Cow<'_, T> where T::Owned: TryConsume<T> {

    fn try_consume_unsized<U>(self, f: impl FnOnce(*mut T) -> U) -> Result<U, Self> {
        if let Cow::Owned(owned) = self {
            owned.try_consume_unsized(f).map_err(|x| Cow::Owned(x))
        } else {
            Err(self)
        }
    }

    fn try_into_owned(self) -> Result<T::Owned, Self> {
        if let Cow::Owned(owned) = self {
            Ok(owned)
        } else {
            Err(self)
        }
    }
}

impl<T: ToOwned + ?Sized, U> FromConsume<U> for Cow<'_, T> where T::Owned: FromConsume<U> {
    unsafe fn from_consume_raw(p: *mut U) -> Self {
        Cow::Owned(<T::Owned as FromConsume<U>>::from_consume_raw(p))
    }
}

/// will always fail
unsafe impl<T> TryConsume<T> for &T {
    fn try_consume_unsized<U>(self, _: impl FnOnce(*mut T) -> U) -> Result<U, Self> {
        Err(self)
    }
}

/// will always fail
unsafe impl<T> TryConsume<T> for &mut T {
    fn try_consume_unsized<U>(self, _: impl FnOnce(*mut T) -> U) -> Result<U, Self> {
        Err(self)
    }
}