mut_set

Use the idea of readonly to implement HashSet with iter_mut.

Add crates by following command

cargo add mut_set mut_set_derive

or add it into Cargo.toml

[dependencies]
mut_set = "0.2"
mut_set_derive = "0.2"

Demo

#[derive(Debug)]
#[mut_set_derive::item]
pub(super) struct MyItem<T1, T2>
where
    T1: Sized,
{
    #[id]
    pub id1: usize,
    pub ctx1: T1,
    pub(in crate::derive) ctx2: T2,
    #[id]
    pub id2: String,
}

#[test]
fn test() {
    let mut set = mut_set::MutSet::new();
    println!("{:?}", set);
    set.insert(MyItem {
        id1: 2,
        id2: "www".to_string(),
        ctx1: -1,
        ctx2: "ccc".to_string(),
    });
    set.insert(MyItem {
        id1: 1,
        id2: "ww".to_string(),
        ctx1: -2,
        ctx2: "cc".to_string(),
    });
    println!("{:?}", set);
    for v in set.iter() {
        println!("{:?}", v);
    }
    for v in set.iter_mut() {
        v.ctx1 = 0;
        println!("{:?}", v.id1);
        // In `iter_mut` IDs write will be prohibited
        // v.id1 = 0;
    }
    println!("{:?}", set);
    let id1 = MyItem::id(2, "www".to_string());
    println!("{:?}", set.get(&id1));
    for v in set.into_iter() {
        println!("{:?}", v);
    }
}

How does mut_set implement

The macro will implement all stuffs in tests/src/prototype.rs.

Take xxx as an example:

• Create two struct xxxImmutId, and xxxId. Where xxxImmutId is same to xxx with private id fields, and xxxId only contains id fields.
• Do rearrangement so that all id fields are located at beginning of the structure. By the help of #[repr(C)], we can use raw pointer operations to (zero-cost?) convert xxx, xxxImmutId, and xxxId.
• impl mut_set::Item for xxx<ItemImmutId = xxxImmutId>
• MutSet<T: Item> = HashMap<u64, T::ItemImmutId>, where the u64 is the hash value.
• Wrap the iteration function
  • iter(&self) -> Iter<&xxx>
  • into_iter(self) -> Iter<xxx>
  • iter_mut(&mut self) -> Iter<&mut xxxImmutId>