Struct VecExtent 

pub struct VecExtent { /* private fields */ }

A validated Vec length: a non-negative item count the runtime can actually allocate.

The third of ADR-041 decision 1’s validated newtypes, beside GridExtent and BitIndex, and it exists for the same reason they do: Vec(n, fill) (ADR-146) takes a user-supplied Int to a vec![fill; n], so n = -1 would cast to usize::MAX and ask the host for 147 exabytes — an OOM abort raised inside an extern "C" function, which the program that caused it never gets to see. praxis_vec_filled cannot reach the allocation without one of these, so the guard is not something a caller can forget.

Implementations

impl VecExtent

pub const MAX_ITEMS: usize = GridExtent::MAX_CELLS

The longest Vec the runtime will construct at a stroke: 2^28 items, which is GridExtent::MAX_CELLS and is 2 GiB of GcRef storage before a single element object exists.

The same number as a grid’s for the same reason ADR-041 decision 2 gave: a cell of one and an item of the other are the same eight bytes, and a count that merely fits in a usize is still an allocation no host can serve. push is not bounded by this and does not need to be — it grows one item at a time, so there is no single multiplication to overflow.

pub const fn new(len: i64) -> Option<VecExtent>

The extent len names, or None if it is negative or exceeds MAX_ITEMS. Zero is legal and names the empty Vec.

pub const fn len(self) -> usize

The item count, proven allocatable.

pub const fn is_empty(self) -> bool

Whether the extent names the empty Vec. Present because clippy asks any type with a len for it, and it is the honest answer.

Trait Implementations

impl Clone for VecExtent

fn clone(&self) -> VecExtent

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for VecExtent

impl Debug for VecExtent

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

Formats the value using the given formatter.

impl Eq for VecExtent

impl PartialEq for VecExtent

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for VecExtent