Struct ink_storage::Lazy

pub struct Lazy<V, KeyType: StorageKey = AutoKey> { /* private fields */ }

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,

pub const fn new() -> Self

Creates a new empty Lazy.

impl<V, KeyType> Lazy<V, KeyType>where
    V: Storable,
    KeyType: StorageKey,

pub fn get(&self) -> Option<V>

Reads the value from the contract storage, if it exists.

pub fn set(&mut self, value: &V)

Writes the given value to the contract storage.

impl<V, KeyType> Lazy<V, KeyType>where
    V: Storable + Default,
    KeyType: StorageKey,

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,

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

Formats the value using the given formatter.

impl<V, KeyType> Default for Lazy<V, KeyType>where
    KeyType: StorageKey,

We implement this manually because the derived implementation adds trait bounds.

fn default() -> Self

Returns the “default value” for a type.

impl<V, KeyType> Storable for Lazy<V, KeyType>where
    KeyType: StorageKey,

fn encode<T: Output + ?Sized>(&self, _dest: &mut T)

Convert self to a slice and append it to the destination.

fn decode<I: Input>(_input: &mut I) -> Result<Self, Error>

Attempt to deserialize the value from input.

impl<V, Key, InnerKey> StorableHint<Key> for Lazy<V, InnerKey>where
    Key: StorageKey,
    InnerKey: StorageKey,
    V: StorableHint<Key>,

type Type = Lazy<<V as StorableHint<Key>>::Type, Key>

Storable type with storage key inside.

type PreferredKey = InnerKey

The storage key that the type prefers. It can be overwritten by an auto-generated storage key.

impl<V, KeyType> StorageKey for Lazy<V, KeyType>where
    KeyType: StorageKey,

const KEY: Key = KeyType::KEY

Storage key of the type.

fn key(&self) -> u32

Returns the storage key.

impl<V, KeyType> StorageLayout for Lazy<V, KeyType>where
    V: StorageLayout + TypeInfo + 'static,
    KeyType: StorageKey + TypeInfo + 'static,

fn layout(_: &Key) -> Layout

Returns the static storage layout of Self.

impl<V, KeyType> TypeInfo for Lazy<V, KeyType>where
    PhantomData<fn() -> (V, KeyType)>: TypeInfo + 'static,
    V: TypeInfo + 'static,
    KeyType: StorageKey + TypeInfo + 'static,

type Identity = Lazy<V, KeyType>

The type identifying for which type info is provided.

fn type_info() -> Type

Returns the static type identifier for Self.