[−][src]Trait frame_support::storage::StorageValue

pub trait StorageValue<T: FullCodec> {
    type Query;
    fn hashed_key() -> [u8; 32];

    fn exists() -> bool;

    fn get() -> Self::Query;

    fn try_get() -> Result<T, ()>;

    fn translate<O: Decode, F: FnOnce(Option<O>) -> Option<T>>(
        f: F
    ) -> Result<Option<T>, ()>;

    fn put<Arg: EncodeLike<T>>(val: Arg);

    fn mutate<R, F: FnOnce(&mut Self::Query) -> R>(f: F) -> R;

    fn kill();

    fn take() -> Self::Query;

    fn append<Items, Item, EncodeLikeItem>(
        items: Items
    ) -> Result<(), &'static str>
    where
        Item: Encode,
        EncodeLikeItem: EncodeLike<Item>,
        T: EncodeAppend<Item = Item>,
        Items: IntoIterator<Item = EncodeLikeItem>,
        Items::IntoIter: ExactSizeIterator;

    fn append_or_put<Items, Item, EncodeLikeItem>(items: Items)
    where
        Item: Encode,
        EncodeLikeItem: EncodeLike<Item>,
        T: EncodeAppend<Item = Item>,
        Items: IntoIterator<Item = EncodeLikeItem> + Clone + EncodeLike<T>,
        Items::IntoIter: ExactSizeIterator;

    fn decode_len() -> Result<usize, &'static str>
    where
        T: DecodeLength + Len;
}

A trait for working with macro-generated storage values under the substrate storage API.

Details on implementation can be found at [generator::StorageValue]

Associated Types

type Query

The type that get/take return.

Loading content...

Required methods

fn hashed_key() -> [u8; 32]

Get the storage key.

fn exists() -> bool

Does the value (explicitly) exist in storage?

fn get() -> Self::Query

Load the value from the provided storage instance.

fn try_get() -> Result<T, ()>

Try to get the underlying value from the provided storage instance; Ok if it exists, Err if not.

fn translate<O: Decode, F: FnOnce(Option<O>) -> Option<T>>(
    f: F
) -> Result<Option<T>, ()>

Translate a value from some previous type (O) to the current type.

f: F is the translation function.

Returns Err if the storage item could not be interpreted as the old type, and Ok, along with the new value if it could.

NOTE: This operates from and to Option<_> types; no effort is made to respect the default value of the original type.

Warning

This function must be used with care, before being updated the storage still contains the old type, thus other calls (such as get) will fail at decoding it.

Usage

This would typically be called inside the module implementation of on_initialize, while ensuring no usage of this storage are made before the call to on_initialize. (More precisely prior initialized modules doesn't make use of this storage).

fn put<Arg: EncodeLike<T>>(val: Arg)

Store a value under this key into the provided storage instance.

fn mutate<R, F: FnOnce(&mut Self::Query) -> R>(f: F) -> R

Mutate the value

fn kill()

Clear the storage value.

fn take() -> Self::Query

Take a value from storage, removing it afterwards.

fn append<Items, Item, EncodeLikeItem>(items: Items) -> Result<(), &'static str> where
    Item: Encode,
    EncodeLikeItem: EncodeLike<Item>,
    T: EncodeAppend<Item = Item>,
    Items: IntoIterator<Item = EncodeLikeItem>,
    Items::IntoIter: ExactSizeIterator, 

Append the given item to the value in the storage.

T is required to implement codec::EncodeAppend.

fn append_or_put<Items, Item, EncodeLikeItem>(items: Items) where
    Item: Encode,
    EncodeLikeItem: EncodeLike<Item>,
    T: EncodeAppend<Item = Item>,
    Items: IntoIterator<Item = EncodeLikeItem> + Clone + EncodeLike<T>,
    Items::IntoIter: ExactSizeIterator, 

Append the given items to the value in the storage.

T is required to implement Codec::EncodeAppend.

Upon any failure, it replaces items as the new value (assuming that the previous stored data is simply corrupt and no longer usable).

WARNING

use with care; if your use-case is not exactly as what this function is doing, you should use append and sensibly handle failure within the runtime code if it happens.

fn decode_len() -> Result<usize, &'static str> where
    T: DecodeLength + Len, 

Read the length of the value in a fast way, without decoding the entire value.

T is required to implement Codec::DecodeLength.

Loading content...

Implementors

impl<T: FullCodec, G: StorageValue<T>> StorageValue<T> for G[src]

type Query = G::Query

fn append<Items, Item, EncodeLikeItem>(items: Items) -> Result<(), &'static str> where
    Item: Encode,
    EncodeLikeItem: EncodeLike<Item>,
    T: EncodeAppend<Item = Item>,
    Items: IntoIterator<Item = EncodeLikeItem>,
    Items::IntoIter: ExactSizeIterator, [src]

Append the given items to the value in the storage.

T is required to implement codec::EncodeAppend.

fn append_or_put<Items, Item, EncodeLikeItem>(items: Items) where
    Item: Encode,
    EncodeLikeItem: EncodeLike<Item>,
    T: EncodeAppend<Item = Item>,
    Items: IntoIterator<Item = EncodeLikeItem> + Clone + EncodeLike<T>,
    Items::IntoIter: ExactSizeIterator, [src]

Safely append the given items to the value in the storage. If a codec error occurs, then the old (presumably corrupt) value is replaced with the given items.

T is required to implement codec::EncodeAppend.

fn decode_len() -> Result<usize, &'static str> where
    T: DecodeLength,
    T: Len, [src]

Read the length of the value in a fast way, without decoding the entire value.

T is required to implement Codec::DecodeLength.

Note that 0 is returned as the default value if no encoded value exists at the given key. Therefore, this function cannot be used as a sign of existence. use the ::exists() function for this purpose.

Loading content...