Struct stack_graphs::arena::SupplementalArena [−][src]
pub struct SupplementalArena<H, T> { /* fields omitted */ }Expand description
A supplemental arena lets you store additional data about some data type that is itself stored
in an Arena.
We implement Index and IndexMut for a more ergonomic syntax. Please note that when
indexing in an immutable context, we panic if you try to access data for a handle that
doesn’t exist in the arena. (Use the get method if you don’t know whether the value
exists or not.) In a mutable context, we automatically create a Default instance of the
type if there isn’t already an instance for that handle in the arena.
// We need an Arena to create handles.
let mut arena = Arena::<u32>::new();
let handle = arena.add(1);
let mut supplemental = SupplementalArena::<u32, String>::new();
// But indexing will panic if the element doesn't already exist.
// assert_eq!(supplemental[handle].as_str(), "");
// The `get` method is always safe, since it returns an Option.
assert_eq!(supplemental.get(handle), None);
// Once we've added the element to the supplemental arena, indexing
// won't panic anymore.
supplemental[handle] = "hello".to_string();
assert_eq!(supplemental[handle].as_str(), "hello");Implementations
Creates a new, empty supplemental arena.
Creates a new, empty supplemental arena, preallocating enough space to store supplemental data for all of the instances that have already been allocated in a (regular) arena.
Returns the item belonging to a particular handle, if it exists.
Returns a mutable reference to the item belonging to a particular handle, creating it first
(using the type’s Default implementation) if it doesn’t already exist.
Trait Implementations
Returns the “default value” for a type. Read more