Trait frame_support::traits::StoredMap

source · 
pub trait StoredMap<K, T: Default> {
    fn get(k: &K) -> T;
    fn try_mutate_exists<R, E: From<DispatchError>>(
        k: &K,
        f: impl FnOnce(&mut Option<T>) -> Result<R, E>
    ) -> Result<R, E>;

    fn mutate<R>(k: &K, f: impl FnOnce(&mut T) -> R) -> Result<R, DispatchError> { ... }
    fn mutate_exists<R>(
        k: &K,
        f: impl FnOnce(&mut Option<T>) -> R
    ) -> Result<R, DispatchError> { ... }
    fn insert(k: &K, t: T) -> Result<(), DispatchError> { ... }
    fn remove(k: &K) -> Result<(), DispatchError> { ... }
}
Expand description

An abstraction of a value stored within storage, but possibly as part of a larger composite item.

Required Methods§

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

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.

Provided Methods§

Mutate the item.

Examples found in repository?
src/traits/stored_map.rs (line 64)
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	fn insert(k: &K, t: T) -> Result<(), DispatchError> {
		Self::mutate(k, |i| *i = t)
	}

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

This is infallible as long as the value does not get destroyed.

Examples found in repository?
src/traits/stored_map.rs (lines 44-52)
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	fn mutate<R>(k: &K, f: impl FnOnce(&mut T) -> R) -> Result<R, DispatchError> {
		Self::mutate_exists(k, |maybe_account| match maybe_account {
			Some(ref mut account) => f(account),
			x @ None => {
				let mut account = Default::default();
				let r = f(&mut account);
				*x = Some(account);
				r
			},
		})
	}

	/// Mutate the item, removing or resetting to default value if it has been mutated to `None`.
	///
	/// This is infallible as long as the value does not get destroyed.
	fn mutate_exists<R>(k: &K, f: impl FnOnce(&mut Option<T>) -> R) -> Result<R, DispatchError> {
		Self::try_mutate_exists(k, |x| -> Result<R, DispatchError> { Ok(f(x)) })
	}

	/// Set the item to something new.
	fn insert(k: &K, t: T) -> Result<(), DispatchError> {
		Self::mutate(k, |i| *i = t)
	}

	/// Remove the item or otherwise replace it with its default value; we don't care which.
	fn remove(k: &K) -> Result<(), DispatchError> {
		Self::mutate_exists(k, |x| *x = None)
	}

Set the item to something new.

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

Implementors§