Struct exonum_merkledb::ReadonlyFork

pub struct ReadonlyFork<'a>(_);

Readonly wrapper for a Fork.

This wrapper allows to read from index state from the fork in a type-safe manner (it is impossible to accidentally modify data in the index), and without encountering runtime errors when attempting to concurrently get the same index more than once.

Since the wrapper borrows the Fork immutably, it is still possible to access indexes in the fork directly. In this scenario, the caller should be careful that ReadonlyFork does not access the same indexes as the original Fork: this will result in a runtime error (sort of like attempting both an exclusive and a shared borrow from a RefCell or RwLock).

Examples

let db = TemporaryDB::new();
let fork = db.fork();
fork.get_list("list").push(1_u32);
let readonly: ReadonlyFork<'_> = fork.readonly();
let list = readonly.get_list::<_, u32>("list");
assert_eq!(list.get(0), Some(1));
let same_list = readonly.get_list::<_, u32>("list");
// ^-- Does not result in an error!

// Original fork is still accessible.
let mut map = fork.get_map("map");
map.put(&1_u32, "foo".to_string());

There are no write methods in indexes instantiated from ReadonlyFork:

let db = TemporaryDB::new();
let fork = db.fork();
let readonly: ReadonlyFork<'_> = fork.readonly();
let mut list = readonly.get_list("list");
list.push(1_u32); // Won't compile: no `push` method in `ListIndex<ReadonlyFork, u32>`!

Trait Implementations

impl<'a> AsReadonly for ReadonlyFork<'a>

type Readonly = Self

Readonly version of the access.

fn as_readonly(&self) -> Self::Readonly

Performs the conversion.

impl<'a> Clone for ReadonlyFork<'a>

fn clone(&self) -> ReadonlyFork<'a>

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<'a> Copy for ReadonlyFork<'a>

impl<'a> Debug for ReadonlyFork<'a>

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

Formats the value using the given formatter.

impl<'a> From<ReadonlyFork<'a>> for GenericRawAccess<'a>

fn from(ro_fork: ReadonlyFork<'a>) -> Self

Performs the conversion.

impl<'a> IntoErased<'a> for ReadonlyFork<'a>

fn into_erased(self) -> ErasedAccess<'a>

Performs the conversion.

impl<'a> RawAccess for ReadonlyFork<'a>

type Changes = ChangesRef<'a>

Type of the changes() that will be applied to the database.

fn snapshot(&self) -> &dyn Snapshot

Reference to a Snapshot. This is the base relative to which the changes are defined.

fn changes(&self, address: &ResolvedAddress) -> Self::Changes

Returns changes related to specific address compared to the snapshot().