Struct StorageMap 

pub struct StorageMap<V: Codec32> { /* private fields */ }

A persistent key-value map stored in contract storage.

StorageMap provides a HashMap-like interface over contract storage slots. Each entry uses two slots: one for existence check, one for the value.

Type Parameters

• V - Value type, must implement Codec32 for 32-byte encoding

Storage Layout

For each key, two slots are derived:

• derive_slot(namespace, ["map:exists", key]) - Existence flag (1 byte)
• derive_slot(namespace, ["map:value", key]) - Encoded value (32 bytes)

Example

const NS_BALANCES: Namespace = Namespace([1u8; 32]);
let balances = StorageMap::<u64>::new(NS_BALANCES);

// Insert
balances.insert(b"alice", &1000)?;

// Get
let balance = balances.get(b"alice")?.unwrap_or(0);

// Check existence
if balances.contains_key(b"alice")? {
    // Key exists
}

// Remove
balances.remove(b"alice")?;

Implementations

impl<V: Codec32> StorageMap<V>

pub const fn new(namespace: Namespace) -> Self

Creates a new map with the specified namespace.

Arguments

• namespace - Unique 32-byte identifier for this map

pub fn exists_slot_for(&self, key: &[u8]) -> [u8; 32]

Computes the existence slot for a given key.

Returns the storage slot address where the existence flag is stored.

pub fn value_slot_for(&self, key: &[u8]) -> [u8; 32]

Computes the value slot for a given key.

Returns the storage slot address where the encoded value is stored.

pub fn slots_for_key(&self, key: &[u8]) -> ([u8; 32], [u8; 32])

Returns both slots (existence, value) for a given key.

Useful for manifest generation.

pub fn contains_key_in<B: StorageBackend>( &self, backend: &B, key: &[u8], ) -> Result<bool>

Checks if a key exists in the map (with explicit backend).

pub fn get_in<B: StorageBackend>( &self, backend: &B, key: &[u8], ) -> Result<Option<V>>

Gets the value for a key (with explicit backend).

Returns None if the key doesn’t exist.

pub fn insert_in<B: StorageBackend>( &self, backend: &mut B, key: &[u8], value: &V, ) -> Result<()>

Inserts a key-value pair (with explicit backend).

pub fn remove_in<B: StorageBackend>( &self, backend: &mut B, key: &[u8], ) -> Result<()>

Removes a key-value pair (with explicit backend).

pub fn contains_typed_key_in<B: StorageBackend, K: BytesCodec>( &self, backend: &B, key: &K, ) -> Result<bool>

Checks if a typed key exists (with explicit backend).

The key is encoded using BytesCodec before lookup.

pub fn get_typed_key_in<B: StorageBackend, K: BytesCodec>( &self, backend: &B, key: &K, ) -> Result<Option<V>>

Gets the value for a typed key (with explicit backend).

pub fn insert_typed_key_in<B: StorageBackend, K: BytesCodec>( &self, backend: &mut B, key: &K, value: &V, ) -> Result<()>

Inserts a typed key-value pair (with explicit backend).

pub fn remove_typed_key_in<B: StorageBackend, K: BytesCodec>( &self, backend: &mut B, key: &K, ) -> Result<()>

Removes a typed key (with explicit backend).

pub fn contains_key(&self, key: &[u8]) -> Result<bool>

Checks if a key exists (production, uses HostStorage).

pub fn get(&self, key: &[u8]) -> Result<Option<V>>

Gets the value for a key (production, uses HostStorage).

pub fn insert(&self, key: &[u8], value: &V) -> Result<()>

Inserts a key-value pair (production, uses HostStorage).

pub fn remove(&self, key: &[u8]) -> Result<()>

Removes a key-value pair (production, uses HostStorage).

pub fn contains_typed_key<K: BytesCodec>(&self, key: &K) -> Result<bool>

Checks if a typed key exists (production, uses HostStorage).

pub fn get_typed_key<K: BytesCodec>(&self, key: &K) -> Result<Option<V>>

Gets the value for a typed key (production, uses HostStorage).

pub fn insert_typed_key<K: BytesCodec>(&self, key: &K, value: &V) -> Result<()>

Inserts a typed key-value pair (production, uses HostStorage).

pub fn remove_typed_key<K: BytesCodec>(&self, key: &K) -> Result<()>

Removes a typed key (production, uses HostStorage).