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

use std::cell::UnsafeCell;
use std::fmt;
use std::sync::{Arc, Weak};

///WeakSelf is simple way to have a Weak pointer inside a data structure pointing to itself.
///
///
///## Use Case
///
///
///Sometimes you want to create a ```struct``` with a pointer to itself or just some other recursive data structure.
///
///
///```rust ignore
/// struct Foo {
///     me: &Foo
/// }
///
/// impl Foo {
///     pub fn new() -> Foo {
///         let foo = Foo{
///             me: ????
///         };
///         foo
///     }
/// }
///
///```
///
///This create helps you do that:
///
///```rust
/// use weak_self::WeakSelf;
/// use std::sync::{Arc, Weak};
/// pub struct Foo {
///     weak_self: WeakSelf<Foo>
/// }
///
/// impl Foo {
///     pub fn new() -> Arc<Foo> {
///         let foo = Arc::new(Foo{
///             weak_self: WeakSelf::new()
///         });
///         foo.weak_self.init(&foo);
///         foo
///     }
///
///     fn weak(&self) -> Weak<Self> {
///         self.weak_self.get()
///     }
/// }
///
///```
///
///
///
///## Dependencies
///
///This package depends on std only
///
///## Usage
///
///To use WeakSelf, add this to your `Cargo.toml`:
///
///```toml
///[dependencies]
///weakself = "1.0.1"
///```
///
///
///## License
///
///Licensed under the terms of MIT license and the Apache License (Version 2.0).
///
///See [LICENSE-MIT](LICENSE-MIT) and [LICENSE-APACHE](LICENSE-APACHE) for details.
///
pub struct WeakSelf<T: ?Sized> {
    cell: UnsafeCell<Option<Weak<T>>>
}

impl<T: ?Sized> WeakSelf<T> {
    /// Constructs a new empty WeakSelf<T>
    pub fn new() -> WeakSelf<T> {
        WeakSelf {
            cell: UnsafeCell::new(None)
        }
    }


    /// Initialize the WeakSelf<T> with an Arc.
    ///
    /// Note: content must point be the only existing Arc, otherwise this method will panig
    pub fn init(&self, content: &Arc<T>) {
        if Arc::strong_count(content) != 1 || Arc::weak_count(content) != 0 {
            panic!("Exclusive access to Arc<T> is required while initializing WeakSelf<T>");
        }
        let weak = Arc::downgrade(content);
        unsafe {
            *self.cell.get() = Some(weak);
        }
    }

    /// get Some Weak<T> pointer to the content, or None if not yet initialized
    pub fn try_get(&self) -> Option<&Weak<T>> {
        unsafe {
            match *self.cell.get() {
                Some(ref weak) => Some(&weak),
                None => None
            }
        }
    }

    /// get a Weak<T> pointer to the content, or panic if not yet initialized
    pub fn get(&self) -> Weak<T> {
        self.try_get().expect("expected WeakSelf to be initialized").clone()
    }
}

unsafe impl<T: ?Sized + Sync + Send> Sync for WeakSelf<T> {}

unsafe impl<T: ?Sized + Sync + Send> Send for WeakSelf<T> {}


impl<T: ?Sized + fmt::Debug> fmt::Debug for WeakSelf<T> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self.try_get() {
            None => { write!(f, "Empty WeakSelf<T>") }
            Some(weak) => fmt::Debug::fmt(weak, f),
        }
    }
}


impl<T: ?Sized> Default for WeakSelf<T> {
    fn default() -> Self {
        WeakSelf::new()
    }
}