Struct Project

pub struct Project<S, T, E>
where
    S: Tuple,
    T: Tuple,
    E: Expression<S>,
{ /* private fields */ }

Projects the tuples of an inner sub-expression of type S to tuples of type T.

Example:

use codd::{Database, expression::Project};

let mut db = Database::new();
let fruit = db.add_relation::<String>("R").unwrap();

db.insert(&fruit, vec!["Apple".to_string(), "BANANA".to_string(), "cherry".to_string()].into());

let lower = Project::new(
    &fruit,
    |t| t.to_lowercase(), // projecting closure
);

assert_eq!(vec!["apple", "banana", "cherry"], db.evaluate(&lower).unwrap().into_tuples());

Implementations

impl<S, T, E> Project<S, T, E>

where S: Tuple, T: Tuple, E: Expression<S>,

pub fn new<I>(expression: I, mapper: impl FnMut(&S) -> T + 'static) -> Self

where I: IntoExpression<S, E>,

Creates a new Project expression over expression with a closure mapper that projects tuples of expression to the resulting tuples.

pub fn expression(&self) -> &E

Returns a reference to the underlying sub-expression.

Trait Implementations

impl<S, T, E> Clone for Project<S, T, E>

where S: Tuple + Clone, T: Tuple + Clone, E: Expression<S> + Clone,

fn clone(&self) -> Project<S, T, E>

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<S, T, E> Debug for Project<S, T, E>

where S: Tuple, T: Tuple, E: Expression<S>,

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<S, T, E> Expression<T> for Project<S, T, E>

where S: Tuple, T: Tuple, E: Expression<S>,

fn visit<V>(&self, visitor: &mut V)

where V: Visitor,

Visits this expression by a Visitor.

fn builder(&self) -> Builder<T, Self>

Returns an expression builder over this expression.

impl<T: Tuple> From<Project<T, T, Mono<T>>> for Mono<T>

fn from(project: Project<T, T, Mono<T>>) -> Self

Converts to this type from the input type.