Module borrow 

The ledger of who holds a component.

Component values live in UnsafeCells, so the compiler cannot police aliasing between two access paths, and this ledger does. A claim is registered before any reference to a value is handed out and is released when the holder goes away; a claim that overlaps one already held panics, naming both sites. Nothing else checks aliasing at run time.

A claim covers either every row of one archetype, which is what a query over a scope asks for, or one row, which is what a single-entity lookup asks for. Two claims conflict when they name the same component type, at least one of them writes, and they can reach the same row: two single-row claims when they name the same entity, anything else when they name the same archetype.

The archetype granularity is deliberately conservative. A query cannot tell before iterating which rows of a mixed archetype a scope can see, so it claims the whole archetype; a single-entity claim on a row of that archetype is then refused even when the query would not have reached that row. Refusing a pair that would have been fine is the price of never allowing a pair that is not.

Claims are filed under the holder that made them rather than under individual ids, so a holder carries one word of ledger state and releases in one pass.

What a holder claims is what it asked a crate::PlanBuilder for: there is no separate declaration of reached components, so a query cannot claim less than it reads.

Re-exports

use core::any::TypeId; 🔒

use core::panic::Location; 🔒

use crate::entity::Entity; 🔒

use crate::query::Ask; 🔒

use crate::query::Mode; 🔒

use crate::world::World; 🔒

Structs

BorrowLedger 🔒

Every claim currently held on a world’s components.

Claims 🔒

The claims one holder owns, released together when it is dropped.

Lease 🔒

One registered claim.

Enums

Rows 🔒

Which rows a claim covers.

Functions

claim_archetype 🔒

Claim on archetype every component the asks named, shared or exclusive.

claim_row 🔒

Claim on one entity’s row every component the asks named.