lazymut 0.1.2

Similar to LazyCell, but use &mut self to get or initialization
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
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168

#![doc = include_str!("../README.md")]
#![no_std]

use core::{fmt::{self, Debug}, mem::replace};

#[doc = include_str!("../README.md")]
#[derive(Default)]
pub struct LazyMut<T, F = fn() -> T> {
    state: State<T, F>,
}

impl<T: Debug, F> Debug for LazyMut<T, F> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let mut t = f.debug_tuple("LazyMut");
        match self.state.try_get() {
            Some(val) => t.field(val),
            None => t.field(&format_args!("<uninit>")),
        };
        t.finish()
    }
}

impl<T, F> LazyMut<T, F> {
    /// Creates a new [`LazyMut`]
    pub const fn new(f: F) -> Self {
        Self { state: State::Uninit(f) }
    }

    /// Try get inner value reference
    ///
    /// # Examples
    ///
    /// ```
    /// # use lazymut::LazyMut;
    /// let mut lazy_mut = LazyMut::new(|| 3);
    ///
    /// assert_eq!(lazy_mut.try_get(), None);
    /// assert_eq!(lazy_mut.get(), &mut 3);
    /// assert_eq!(lazy_mut.try_get(), Some(&3));
    /// ```
    pub const fn try_get(&self) -> Option<&T> {
        self.state.try_get()
    }

    /// Try get inner value mut reference
    ///
    /// # Examples
    ///
    /// ```
    /// # use lazymut::LazyMut;
    /// let mut lazy_mut = LazyMut::new(|| 3);
    ///
    /// assert_eq!(lazy_mut.try_get_mut(), None);
    /// assert_eq!(lazy_mut.get(), &mut 3);
    /// assert_eq!(lazy_mut.try_get_mut(), Some(&mut 3));
    /// ```
    pub const fn try_get_mut(&mut self) -> Option<&mut T> {
        self.state.try_get_mut()
    }

    /// Returns value when initialized
    ///
    /// # Panics
    ///
    /// Panics if state is poisoned
    ///
    /// # Examples
    ///
    /// ```
    /// # use lazymut::LazyMut;
    /// let mut lazy_mut = LazyMut::new(|| 3);
    ///
    /// assert_eq!(lazy_mut.get(), &mut 3);
    /// assert_eq!(lazy_mut.into_inner(), Some(3));
    /// ```
    ///
    /// ```
    /// # use lazymut::LazyMut;
    /// let mut lazy_mut = LazyMut::new(|| 3i32);
    ///
    /// # assert_ne!(lazy_mut.try_get(), Some(&3));
    /// assert_eq!(lazy_mut.into_inner(), None);
    /// ```
    pub fn into_inner(self) -> Option<T> {
        match self.state {
            State::Uninit(_) => None,
            State::Poisoned => panic_poisoned(),
            State::Inited(val) => Some(val),
        }
    }
}

impl<T, F: FnOnce() -> T> LazyMut<T, F> {
    /// Get mutable value reference or initialize value
    ///
    /// # Panics
    ///
    /// Panics if state is poisoned or initializer panic
    ///
    /// # Examples
    ///
    /// ```
    /// use lazymut::LazyMut;
    ///
    /// let mut lazy_mut = LazyMut::new(|| vec![1]);
    ///
    /// assert_eq!(lazy_mut.get(), &mut vec![1]);
    /// lazy_mut.get().push(2);
    /// assert_eq!(lazy_mut.get(), &mut vec![1, 2]);
    /// ```
    pub fn get(&mut self) -> &mut T {
        self.state.get_or_init()
    }
}

#[derive(Clone)]
enum State<T, F> {
    Uninit(F),
    Inited(T),
    Poisoned,
}

impl<T: Default, F> Default for State<T, F> {
    fn default() -> Self {
        Self::Inited(Default::default())
    }
}

impl<T, F> State<T, F>
where F: FnOnce() -> T,
{
    fn get_or_init(&mut self) -> &mut T {
        match self {
            State::Poisoned => panic_poisoned(),
            State::Inited(val) => val,
            State::Uninit(_) => {
                let this = replace(self, Self::Poisoned);
                let Self::Uninit(f) = this else { unreachable!() };
                *self = State::Inited(f());
                self.try_get_mut().unwrap()
            },
        }
    }
}

impl<T, F> State<T, F> {
    const fn try_get(&self) -> Option<&T> {
        if let Self::Inited(v) = self {
            Some(v)
        } else {
            None
        }
    }

    const fn try_get_mut(&mut self) -> Option<&mut T> {
        if let Self::Inited(v) = self {
            Some(v)
        } else {
            None
        }
    }
}

#[cold]
#[inline(never)]
fn panic_poisoned() -> ! {
    panic!("LazyMut instance has previously been poisoned")
}