Enum Refusal 

pub enum Refusal {
    NoLookup,
    CollectionReadsTheElement,
    KeyReadsMoreThanTheElement,
    PredicateIsNotAnEquality,
    ProjectionReadsMoreThanTheRow,
    NothingSaved,
    NoMembership,
    MembershipAndMore,
}

Why a body that contained a map_get was not recognised as a join.

§99.6’s rule for the case inference cannot see: “compile it the slow way and say so”. These reach crate::plan::Node::because, so beck explain cost prints the reason beside the operator that pays for it rather than leaving a reader to guess which of the conditions failed.

Variants

NoLookup

Nothing in the body that could relate: no map_get and no filter_list.

CollectionReadsTheElement

The collection looked up in is derived per element, so there is nothing to index once.

KeyReadsMoreThanTheElement

The key reads something other than the element, so it is not an equi-join on the left row.

PredicateIsNotAnEquality

The filter’s predicate is not an equality with one side over each element, so there is no key to arrange the collection by.

ProjectionReadsMoreThanTheRow

The aggregate’s projection reads something other than the row it is applied to, so what each row contributes to its group is not a function of that row.

NothingSaved

Recognising it would not remove the capture that costs the rebuild, so it buys nothing.

NoMembership

Nothing in the predicate asks another collection whether it holds a key, so there is no difference and no intersection here.

MembershipAndMore

The predicate asks a collection whether it holds a key and something else besides, so the filter is not the membership test — it contains one.

Implementations

impl Refusal

pub fn because(&self) -> String

The sentence beck explain prints, in the voice the rest of the plan’s reasons use.

Trait Implementations

impl Clone for Refusal

fn clone(&self) -> Refusal

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Refusal

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

Formats the value using the given formatter.

impl PartialEq for Refusal

fn eq(&self, other: &Refusal) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Eq for Refusal

impl StructuralPartialEq for Refusal