codd 0.1.0

codd is a minimal in-memory database with relational algebraic expressions as queries.
Documentation 
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

use super::{Expression, Visitor};
use crate::Tuple;
use std::marker::PhantomData;

/// Is a placeholder for a "full" instance, containing *all* tuples of its type.
///
/// **Note**: because `Full` expression cannot be described by a range-restricted
/// (see [chapter 2] of Foundations of Databases) query, any query containing
/// `Full` as a subexpression cannot be evaluated in a database safely.
///
/// **Example**:
/// ```rust
/// use codd::{Database, expression::Full};
///
/// let mut db = Database::new();
/// let full = Full::<i32>::new();
///
/// assert!(db.evaluate(&full).is_err()); // cannot be evaluated
/// ```
///
/// [chapter 2]: http://webdam.inria.fr/Alice/pdfs/Chapter-5.pdf
#[derive(Clone, Debug)]
pub struct Full<T>
where
    T: Tuple,
{
    _phantom: PhantomData<T>,
}

impl<T> Full<T>
where
    T: Tuple,
{
    /// Creates a new instance of `Full`.
    pub fn new() -> Self {
        Self {
            _phantom: PhantomData,
        }
    }
}

impl<T> Expression<T> for Full<T>
where
    T: Tuple,
{
    fn visit<V>(&self, visitor: &mut V)
    where
        V: Visitor,
    {
        visitor.visit_full(&self);
    }
}

impl<T: Tuple> Default for Full<T> {
    fn default() -> Self {
        Self::new()
    }
}