Struct polkadot_sdk_frame::traits::StorageMapShim

pub struct StorageMapShim<S, K, T>(/* private fields */);

A shim for placing around a storage item in order to use it as a StoredValue. Ideally this wouldn’t be needed as StorageValues should blanket implement StoredValues, however this would break the ability to have custom impls of StoredValue. The other workaround is to implement it directly in the macro.

This form has the advantage that two additional types are provides, Created and Removed, which are both generic events that can be tied to handlers to do something in the case of being about to create an account where one didn’t previously exist (at all; not just where it used to be the default value), or where the account is being removed or reset back to the default value where previously it did exist (though may have been in a default state). This works well with system module’s CallOnCreatedAccount and CallKillAccount.

Trait Implementations

impl<S, K, T> StoredMap<K, T> for StorageMapShim<S, K, T>

where S: StorageMap<K, T, Query = T>, K: FullCodec, T: FullCodec + Default,

fn get(k: &K) -> T

Get the item, or its default if it doesn’t yet exist; we make no distinction between the two.

fn insert(k: &K, t: T) -> Result<(), DispatchError>

Set the item to something new.

fn remove(k: &K) -> Result<(), DispatchError>

Remove the item or otherwise replace it with its default value; we don’t care which.

fn mutate<R>(k: &K, f: impl FnOnce(&mut T) -> R) -> Result<R, DispatchError>

Mutate the item.

fn mutate_exists<R>( k: &K, f: impl FnOnce(&mut Option<T>) -> R, ) -> Result<R, DispatchError>

Mutate the item, removing or resetting to default value if it has been mutated to None.

fn try_mutate_exists<R, E>( k: &K, f: impl FnOnce(&mut Option<T>) -> Result<R, E>, ) -> Result<R, E>

where E: From<DispatchError>,

Maybe mutate the item only if an Ok value is returned from f. Do nothing if an Err is returned. It is removed or reset to default value if it has been mutated to None. f will always be called with an option representing if the storage item exists (Some<V>) or if the storage item does not exist (None), independent of the QueryType.