Struct LoopHeader 

pub struct LoopHeader { /* private fields */ }

All the bindings made in a loop, which are visible to the entire loop via “loop header definitions” (a.k.a. loop-back bindings)

Loop control flow analysis needs a way for uses early in the loop to see bindings that come later, reflecting the fact that a previous iteration of the loop might’ve already executed those bindings. For example:

x = "A"
while some_condition():
    # The loop entry value (in the first iteration) and the following binding (in other
    # iterations) are both visible at this use.
    reveal_type(x)  # revealed: Literal["A", "B"]
    x = "B"

As an important special case, these loop header definitions also combine with fixpoint iteration to let us infer int for loop variables. For example:

i = 0  # revealed: Literal[0]
while i < 1_000_000:
    i += 1  # revealed: int

The add-assign statement i += 1 is both a use and a binding. The use sees the i = 0 binding at the top, and it also sees itself via the loop header definition of i. When we infer the type of i in or after the loop, fixpoint iteration produces an ever-expanding union of literals (Literal[0, 1, 2, ...]) until we eventually reach the threshold for widening to int and stop iterating. (See should_widen and widen_literal_types.)

Loop header definitions are synthesized before walking the loop body, but the bindings in the header are only known after walking all loop-back edges. The builder reserves a LoopHeaderId before the walk, fills the corresponding header afterward, and publishes the completed headers in the scope’s UseDefMap.

Implementations

impl LoopHeader

pub fn bindings_for_place( &self, place: ScopedPlaceId, ) -> impl Iterator<Item = LiveBinding> + '_

Trait Implementations

impl Clone for LoopHeader

fn clone(&self) -> LoopHeader

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for LoopHeader

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

Formats the value using the given formatter.

impl Default for LoopHeader

fn default() -> LoopHeader

Returns the “default value” for a type.

impl Eq for LoopHeader

impl GetSize for LoopHeader

fn get_heap_size(&self) -> usize

Determines how many bytes this object occupies inside the heap.

fn get_heap_size_with_tracker<TRACKER: GetSizeTracker>( &self, tracker: TRACKER, ) -> (usize, TRACKER)

Determines how many bytes this object occupies inside the heap while using a tracker.

fn get_stack_size() -> usize

Determines how may bytes this object occupies inside the stack.

fn get_size(&self) -> usize

Determines the total size of the object.

fn get_size_with_tracker<T>(&self, tracker: T) -> (usize, T)

where T: GetSizeTracker,

Determines the total size of the object while using a tracker.

impl PartialEq for LoopHeader

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for LoopHeader