Enum Use 

pub enum Use {
    Answer,
    Enable,
    Decide,
}

What a caller intends to do with an answer.

The three uses of spec/stats/05-every-query.md section 5.1.1. A consumer declares one, the class rule follows from it rather than from the consumer’s judgement, and EXPLAIN prints which one happened. See Stat::answer, Stat::enable and Stat::decide.

Variants

Answer

The statistic is the result. Entitled to Exact, and to Certified where the consumer can discharge the proof obligation and has a fallback for when it cannot.

Enable

The statistic licenses a rewrite that would be wrong if the statistic were wrong. Entitled to Exact only.

Decide

The statistic chooses between two plans that produce the same rows. Entitled to any class, including none.

Implementations

impl Use

pub const fn name(self) -> &'static str

The word EXPLAIN prints.

pub const fn permits(self, class: Option<Class>) -> bool

Whether a class is enough for this use.

Answer says yes to a certificate here and the caller still has to discharge it, which is what Stat::answer_certified is for. This function is the class rule and not the whole obligation.

Trait Implementations

impl Clone for Use

fn clone(&self) -> Use

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for Use

impl Debug for Use

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

Formats the value using the given formatter.

impl Display for Use

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

Formats the value using the given formatter.

impl Eq for Use

impl Hash for Use

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl PartialEq for Use

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for Use