Struct Query

pub struct Query<Q, U, D, R>
where
    Q: FnMut(&U) -> R,
    D: FnMut() -> R,
{ /* private fields */ }

A query non-destructively creates some value R from references to a U. It can be called on values of any type T, not just on values of type U, so it requires a default R value for when it is called on values which are not a T.

This essentially lifts a FnMut(&U) -> R into a for<T> FnMut(&T) -> R.

Implementations

impl<Q, U, R> Query<Q, U, fn() -> R, R>

where Q: FnMut(&U) -> R, R: Default,

pub fn new(query: Q) -> Query<Q, U, fn() -> R, R>

Construct a new Query, returning R::default() for the cases where we query a value whose type is not U.

impl<Q, U, D, R> Query<Q, U, D, R>

where Q: FnMut(&U) -> R, D: FnMut() -> R,

pub fn or_else(make_default: D, query: Q) -> Query<Q, U, D, R>

Construct a new Query, returning make_default() for the cases where we query a value whose type is not U.

Trait Implementations

impl<Q, U: Debug, D, R: Debug> Debug for Query<Q, U, D, R>

where Q: FnMut(&U) -> R + Debug, D: FnMut() -> R + Debug,

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

Formats the value using the given formatter.

impl<Q, U, D, R> GenericQuery<R> for Query<Q, U, D, R>

where Q: FnMut(&U) -> R, D: FnMut() -> R,

fn query<T>(&mut self, t: &T) -> R

where T: Term,

Call the query function on any T.