ijson 0.1.7

A more memory efficient replacement for serde_json::Value
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107

use std::marker::PhantomData;
use std::ops::{Deref, DerefMut};
use std::ptr::NonNull;

#[repr(transparent)]
pub(crate) struct ThinRef<'a, T> {
    ptr: NonNull<T>,
    phantom: PhantomData<&'a T>,
}

impl<T> ThinRef<'_, T> {
    /// Safety: `ptr` must point to a valid, initialised `T` that stays valid for `'a`
    /// and is not mutably aliased for `'a` — a `ThinRef` hands out shared `&T` borrows,
    /// so a concurrent `&mut T` (or `ThinMut`) to the same `T` would be UB.
    pub(crate) unsafe fn new(ptr: NonNull<T>) -> Self {
        Self {
            ptr,
            phantom: PhantomData,
        }
    }
}

impl<T> Deref for ThinRef<'_, T> {
    type Target = T;

    fn deref(&self) -> &Self::Target {
        // Safety: `ptr` is valid for `'a` and unaliased by `ThinRef::new`'s contract.
        unsafe { &*self.ptr() }
    }
}

impl<T> Copy for ThinRef<'_, T> {}
impl<T> Clone for ThinRef<'_, T> {
    fn clone(&self) -> Self {
        *self
    }
}

#[repr(transparent)]
pub(crate) struct ThinMut<'a, T> {
    ptr: NonNull<T>,
    phantom: PhantomData<&'a mut T>,
}

impl<T> ThinMut<'_, T> {
    /// Safety: `ptr` must point to a valid, initialised `T` that stays valid for `'a`,
    /// and the referent must be *exclusively* borrowed for `'a` — no other live
    /// `ThinRef`, `ThinMut`, `&T`, or `&mut T` may alias it. (`ThinMut` hands out
    /// `&mut T` through `DerefMut`, so a second view of the same `T` would be UB.)
    pub(crate) unsafe fn new(ptr: NonNull<T>) -> Self {
        Self {
            ptr,
            phantom: PhantomData,
        }
    }
}

impl<T> Deref for ThinMut<'_, T> {
    type Target = T;

    fn deref(&self) -> &Self::Target {
        // Safety: `ptr` must be valid
        unsafe { &*self.ptr() }
    }
}

impl<T> DerefMut for ThinMut<'_, T> {
    fn deref_mut(&mut self) -> &mut Self::Target {
        // Safety: `ptr` must be valid
        unsafe { &mut *self.ptr_mut() }
    }
}

pub(crate) trait ThinRefExt<'a, T>: Deref<Target = T> {
    fn ptr(&self) -> *const T;
}

pub(crate) trait ThinMutExt<'a, T>:
    DerefMut<Target = T> + ThinRefExt<'a, T> + Sized
{
    fn ptr_mut(&mut self) -> *mut T;
    fn reborrow<'b>(&'b mut self) -> ThinMut<'b, T>;
}

impl<'a, T> ThinRefExt<'a, T> for ThinRef<'a, T> {
    fn ptr(&self) -> *const T {
        self.ptr.as_ptr()
    }
}

impl<'a, T> ThinRefExt<'a, T> for ThinMut<'a, T> {
    fn ptr(&self) -> *const T {
        self.ptr.as_ptr()
    }
}

impl<'a, T> ThinMutExt<'a, T> for ThinMut<'a, T> {
    fn ptr_mut(&mut self) -> *mut T {
        self.ptr.as_ptr()
    }
    fn reborrow<'b>(&'b mut self) -> ThinMut<'b, T> {
        Self {
            ptr: self.ptr,
            phantom: self.phantom,
        }
    }
}