Struct mz_transform::analysis::equivalences::EquivalenceClasses

pub struct EquivalenceClasses {
    pub classes: Vec<Vec<MirScalarExpr>>,
}

A compact representation of classes of expressions that must be equivalent.

Each “class” contains a list of expressions, each of which must be Eq::eq equal. Ideally, the first element is the “simplest”, e.g. a literal or column reference, and any other element of that list can be replaced by it.

The classes are meant to be minimized, with each expression as reduced as it can be, and all classes sharing an element merged.

Fields

classes: Vec<Vec<MirScalarExpr>>

Multiple lists of equivalent expressions, each representing an equivalence class.

The first element should be the “canonical” simplest element, that any other element can be replaced by. These classes are unified whenever possible, to minimize the number of classes.

Implementations

impl EquivalenceClasses

pub fn minimize(&mut self, columns: &Option<Vec<ColumnType>>)

Update self to maintain the same equivalences which potentially reducing along Ord::le.

Informally this means simplifying constraints, removing redundant constraints, and unifying equivalence classes.

pub fn union(&self, other: &Self) -> Self

Produce the equivalences present in both inputs.

pub fn permute(&mut self, permutation: &[usize])

Permutes each expression, looking up each column reference in permutation and replacing with what it finds.

pub fn project<I>(&mut self, output_columns: I)

where I: IntoIterator<Item = usize> + Clone,

Subject the constraints to the column projection, reworking and removing equivalences.

This method should also introduce equivalences representing any repeated columns.

pub fn reduce_expr(&self, expr: &mut MirScalarExpr) -> bool

Perform any simplification, report if effective.

pub fn reduce_child(&self, expr: &mut MirScalarExpr) -> bool

Perform any simplification on children, report if effective.

pub fn unsatisfiable(&self) -> bool

True if any equivalence class contains two distinct non-error literals.

Trait Implementations

impl Clone for EquivalenceClasses

fn clone(&self) -> EquivalenceClasses

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for EquivalenceClasses

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

Formats the value using the given formatter.

impl Default for EquivalenceClasses

fn default() -> EquivalenceClasses

Returns the “default value” for a type.

impl Ord for EquivalenceClasses

fn cmp(&self, other: &EquivalenceClasses) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized + PartialOrd,

Restrict a value to a certain interval.

impl PartialEq for EquivalenceClasses

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

This method tests for self and other values to be equal, and is used by ==.

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

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

impl PartialOrd for EquivalenceClasses

fn partial_cmp(&self, other: &EquivalenceClasses) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

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

This method tests less than (for self and other) and is used by the < operator.

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

This method tests less than or equal to (for self and other) and is used by the <= operator.

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

This method tests greater than (for self and other) and is used by the > operator.

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

This method tests greater than or equal to (for self and other) and is used by the >= operator.

impl Eq for EquivalenceClasses

impl StructuralPartialEq for EquivalenceClasses