ideal 0.7.4

When you need some ids.
Documentation 
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use std::marker::PhantomData;
use std::u32::MAX;
use std::hash;
use std::fmt;
use std::cmp::Ordering;

#[derive(Serialize, Deserialize)]
pub struct Id<T> {
    index: u32,
    #[serde(skip)]
    marker: PhantomData<T>,
}

impl<T> Id<T> {
    pub fn invalid() -> Self {
        Self::new(MAX)
    }

    pub fn is_invalid(&self) -> bool {
        self.index == MAX
    }

    pub fn is_valid(&self) -> bool {
        self.index != MAX
    }

    pub fn cast<U>(&self) -> Id<U> {
        Id::new(self.index)
    }

    fn new(index: u32) -> Self {
        Self { index, marker: PhantomData }
    }
}

impl<T> Copy for Id<T> {}

impl<T> Clone for Id<T> {
    fn clone(&self) -> Self {
        *self
    }
}

impl<T> PartialEq for Id<T> {
    fn eq(&self, other: &Self) -> bool {
        self.index == other.index
    }
}

impl<T> Eq for Id<T> {}

impl<T> PartialOrd for Id<T> {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        self.index.partial_cmp(&other.index)
    }
}

impl<T> Ord for Id<T> {
    fn cmp(&self, other: &Self) -> Ordering {
        self.index.cmp(&other.index)
    }
}

impl<T> hash::Hash for Id<T> {
    fn hash<H: hash::Hasher>(&self, hasher: &mut H) {
        self.index.hash(hasher);
    }
}

impl<T> fmt::Debug for Id<T> {
    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        write!(formatter, "Id[{}]", self.index)
    }
}

impl<T> From<usize> for Id<T> {
    fn from(index: usize) -> Self {
        if index >= MAX as usize {
            Self::invalid()
        } else {
            Self::new(index as u32)
        }
    }
}

impl<T> Into<usize> for Id<T> {
    fn into(self) -> usize {
        self.index as usize
    }
}