pub struct Lazy<V, KeyType = AutoKey>where
KeyType: StorageKey,{ /* private fields */ }
Expand description
A simple wrapper around a type to store it in a separate storage cell under its own
storage key. If you want to update the value, first you need to
get
it, update the value, and then call
set
with the new value.
Important
The wrapper requires its own pre-defined storage key in order to determine where it
stores value. By default, the is automatically calculated using
AutoKey
during compilation. However, anyone can specify a
storage key using ManualKey
. Specifying the storage key
can be helpful for upgradeable contracts or you want to be resistant to future changes
of storage key calculation strategy.
Note
If the contract has two or more Lazy
with the same storage key, modifying the value
of one of them will modify others.
This is an example of how you can do this:
use ink::storage::{
traits::ManualKey,
Lazy,
};
#[ink(storage)]
#[derive(Default)]
pub struct MyContract {
owner: Lazy<AccountId>,
balance: Lazy<Balance, ManualKey<123>>,
}
impl MyContract {
#[ink(constructor)]
pub fn new() -> Self {
let mut instance = Self::default();
let caller = Self::env().caller();
instance.owner.set(&caller);
instance.balance.set(&123456);
instance
}
}
Implementations§
§impl<V, KeyType> Lazy<V, KeyType>where
KeyType: StorageKey,
impl<V, KeyType> Lazy<V, KeyType>where KeyType: StorageKey,
§impl<V, KeyType> Lazy<V, KeyType>where
V: Storable,
KeyType: StorageKey,
impl<V, KeyType> Lazy<V, KeyType>where V: Storable, KeyType: StorageKey,
pub fn get(&self) -> Option<V>
pub fn get(&self) -> Option<V>
Reads the value
from the contract storage, if it exists.
Panics
Traps if the encoded value
doesn’t fit into the static buffer.
pub fn try_get(&self) -> Option<Result<V, Error>>
pub fn try_get(&self) -> Option<Result<V, Error>>
Try to read the value
from the contract storage.
To successfully retrieve the value
, the encoded key
and value
must both fit into the static buffer together.
Returns:
Some(Ok(_))
ifvalue
was received from storage and could be decoded.Some(Err(_))
if retrieving thevalue
would exceed the static buffer size.None
if there was no value under this storage key.
§impl<V, KeyType> Lazy<V, KeyType>where
V: Storable + Default,
KeyType: StorageKey,
impl<V, KeyType> Lazy<V, KeyType>where V: Storable + Default, KeyType: StorageKey,
pub fn get_or_default(&self) -> V
pub fn get_or_default(&self) -> V
Reads the value
from the contract storage.
Returns the default value for the storage type if no value
exists.
Trait Implementations§
§impl<V, KeyType> Debug for Lazy<V, KeyType>where
KeyType: StorageKey,
impl<V, KeyType> Debug for Lazy<V, KeyType>where KeyType: StorageKey,
§impl<V, KeyType> Default for Lazy<V, KeyType>where
KeyType: StorageKey,
impl<V, KeyType> Default for Lazy<V, KeyType>where KeyType: StorageKey,
We implement this manually because the derived implementation adds trait bounds.