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

// Originally from https://github.com/http-rs/http-types/blob/main/src/extensions.rs
//
// Implementation is based on
// - https://github.com/hyperium/http/blob/master/src/extensions.rs
// - https://github.com/kardeiz/type-map/blob/master/src/lib.rs
use hashbrown::HashMap;
use std::{
    any::{Any, TypeId},
    fmt,
    hash::{BuildHasherDefault, Hasher},
};

/// Store and retrieve values by
/// [`TypeId`](https://doc.rust-lang.org/std/any/struct.TypeId.html). This
/// allows storing arbitrary data that implements `Sync + Send +
/// 'static`.
#[derive(Default)]
pub struct StateSet(HashMap<TypeId, Box<dyn Any + Send + Sync>, BuildHasherDefault<IdHasher>>);

impl StateSet {
    /// Create an empty `StateSet`.
    pub fn new() -> Self {
        Self::default()
    }

    /// Insert a value into this `StateSet`.
    ///
    /// If a value of this type already exists, it will be returned.
    pub fn insert<T: Send + Sync + 'static>(&mut self, val: T) -> Option<T> {
        self.0
            .insert(TypeId::of::<T>(), Box::new(val))
            .and_then(|boxed| (boxed as Box<dyn Any>).downcast().ok().map(|boxed| *boxed))
    }

    /// Check if container contains value for type
    pub fn contains<T: 'static>(&self) -> bool {
        self.0.get(&TypeId::of::<T>()).is_some()
    }

    /// Get a reference to a value previously inserted on this `StateSet`.
    pub fn get<T: 'static>(&self) -> Option<&T> {
        self.0
            .get(&TypeId::of::<T>())
            .and_then(|boxed| (&**boxed as &(dyn Any)).downcast_ref())
    }

    /// Get a mutable reference to a value previously inserted on this `StateSet`.
    pub fn get_mut<T: 'static>(&mut self) -> Option<&mut T> {
        self.0
            .get_mut(&TypeId::of::<T>())
            .and_then(|boxed| (&mut **boxed as &mut (dyn Any)).downcast_mut())
    }

    /// Remove a value from this `StateSet`.
    ///
    /// If a value of this type exists, it will be returned.
    pub fn take<T: 'static>(&mut self) -> Option<T> {
        self.0
            .remove(&TypeId::of::<T>())
            .and_then(|boxed| (boxed as Box<dyn Any>).downcast().ok().map(|boxed| *boxed))
    }

    /// Gets a value from this `StateSet` or populates it with the
    /// provided default.
    #[allow(clippy::missing_panics_doc)]
    pub fn get_or_insert<T: Send + Sync + 'static>(&mut self, default: T) -> &mut T {
        self.0
            .entry(TypeId::of::<T>())
            .or_insert_with(|| Box::new(default))
            .downcast_mut()
            .expect("StateSet maintains the invariant the value associated with a given TypeId is always the type associated with that TypeId.")
    }

    /// Gets a value from this `StateSet` or populates it with the
    /// provided default function.
    #[allow(clippy::missing_panics_doc)]
    pub fn get_or_insert_with<F, T>(&mut self, default: F) -> &mut T
    where
        F: FnOnce() -> T,
        T: Send + Sync + 'static,
    {
        self.0
            .entry(TypeId::of::<T>())
            .or_insert_with(|| Box::new(default()))
            .downcast_mut()
            .expect("StateSet maintains the invariant the value associated with a given TypeId is always the type associated with that TypeId.")
    }
}

impl fmt::Debug for StateSet {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("StateSet").finish()
    }
}

// With TypeIds as keys, there's no need to hash them. So we simply use an identy hasher.
#[derive(Default)]
struct IdHasher(u64);

impl Hasher for IdHasher {
    fn write(&mut self, _: &[u8]) {
        unreachable!("TypeId calls write_u64");
    }

    #[inline]
    fn write_u64(&mut self, id: u64) {
        self.0 = id;
    }

    #[inline]
    fn finish(&self) -> u64 {
        self.0
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    #[test]
    fn test_extensions() {
        #[derive(Debug, PartialEq)]
        struct MyType(i32);

        let mut map = StateSet::new();

        map.insert(5i32);
        map.insert(MyType(10));

        assert_eq!(map.get(), Some(&5i32));
        assert_eq!(map.get_mut(), Some(&mut 5i32));

        assert_eq!(map.take::<i32>(), Some(5i32));
        assert!(map.get::<i32>().is_none());

        assert_eq!(map.get::<bool>(), None);
        assert_eq!(map.get(), Some(&MyType(10)));
    }
}