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
169
170
171
172
173
174
175

use std::ops::Deref;
use std::borrow::Borrow;
use std::fmt;

/// `HandleIndex` type is arbitrary. Keeping it 32-bits allows for
/// a single 64-bits word per `Handle`.
pub type HandleIndex = u32;

/// `Handle` is made up of two field, `index` and `version`. `index` are
/// usually used to indicated address into some kind of space. This value
/// is recycled when an `Handle` is freed to save address. However, this
/// means that you could end up with two different `Handle` with identical
/// indices. We solve this by introducing `version`.
#[derive(Debug, Default, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct Handle {
    index: HandleIndex,
    version: HandleIndex,
}

impl Handle {
    /// Constructs a new `Handle`.
    #[inline]
    pub fn new(index: HandleIndex, version: HandleIndex) -> Self {
        Handle {
            index: index,
            version: version,
        }
    }

    /// Constructs a nil/uninitialized `Handle`.
    #[inline]
    pub fn nil() -> Self {
        Handle {
            index: 0,
            version: 0,
        }
    }

    /// Returns true if this `Handle` has been initialized.
    #[inline]
    pub fn is_valid(&self) -> bool {
        self.index > 0 || self.version > 0
    }

    /// Invalidate this `Handle` to default value.
    #[inline]
    pub fn invalidate(&mut self) {
        self.index = 0;
        self.version = 0;
    }

    /// Returns index value.
    #[inline]
    pub fn index(&self) -> HandleIndex {
        self.index
    }

    /// Returns version value.
    #[inline]
    pub fn version(&self) -> HandleIndex {
        self.version
    }
}

impl Deref for Handle {
    type Target = HandleIndex;

    fn deref(&self) -> &HandleIndex {
        &self.index
    }
}

impl Borrow<HandleIndex> for Handle {
    fn borrow(&self) -> &HandleIndex {
        &self.index
    }
}

impl<'a> Borrow<HandleIndex> for &'a Handle {
    fn borrow(&self) -> &HandleIndex {
        &self.index
    }
}

impl fmt::Display for Handle {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "Handle ({}, {})", self.index, self.version)
    }
}

#[macro_export]
macro_rules! impl_handle {
    ($name: ident) => (
        #[derive(Debug, Default, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
        pub struct $name ($crate::utils::handle::Handle);

        impl From<$name> for $crate::utils::handle::Handle {
            fn from(handle: $name) -> Self {
                handle.0
            }
        }

        impl From<$crate::utils::handle::Handle> for $name {
            fn from(handle: $crate::utils::handle::Handle) -> Self {
                $name(handle)
            }
        }

        impl ::std::ops::Deref for $name {
            type Target = $crate::utils::handle::Handle;
            fn deref(&self) -> &$crate::utils::handle::Handle {
                &self.0
            }
        }

        impl ::std::borrow::Borrow<$crate::utils::handle::Handle> for $name {
            fn borrow(&self) -> &$crate::utils::handle::Handle {
                &self.0
            }
        }

        impl ::std::fmt::Display for $name {
            fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
                write!(f, "$name ({}, {})", self.index(), self.version())
            }
        }
    )
}

#[cfg(test)]
mod test {
    use super::*;

    #[test]
    fn basic() {
        let mut h2 = Handle::new(2, 4);
        assert_eq!(h2.index, 2);
        assert_eq!(h2.version, 4);
        assert!(h2.is_valid());
        assert_eq!(*h2, 2);

        h2.invalidate();
        assert_eq!(h2.index, 0);
        assert_eq!(h2.version, 0);
        assert!(!h2.is_valid());
        assert_eq!(*h2, 0);
    }

    #[test]
    fn container() {
        use std::collections::HashSet;
        let h1 = Handle::new(1, 1);
        let h2 = Handle::new(1, 2);
        let h3 = Handle::new(2, 2);
        let h4 = Handle::new(1, 1);

        let mut map = HashSet::new();
        assert_eq!(map.insert(h1), true);
        assert_eq!(map.contains(&h1), true);
        assert_eq!(map.insert(h4), false);
        assert_eq!(map.contains(&h4), true);
        assert_eq!(map.insert(h2), true);
        assert_eq!(map.insert(h3), true);
    }

    impl_handle!(TypeSafeHandle);
    #[test]
    fn type_safe_handle() {
        let h1 = TypeSafeHandle::default();
        assert_eq!(h1, TypeSafeHandle::from(Handle::default()));

        let h2 = TypeSafeHandle(Handle::default());
        assert_eq!(*h2, Handle::default());
    }
}