Attribute Macro anchor_lang::prelude::account
source · #[account]Expand description
An attribute for a data structure representing a Solana account.
#[account] generates trait implementations for the following traits:
When implementing account serialization traits the first 8 bytes are reserved for a unique account discriminator, self described by the first 8 bytes of the SHA256 of the account’s Rust ident.
As a result, any calls to AccountDeserialize’s try_deserialize will
check this discriminator. If it doesn’t match, an invalid account was given,
and the account deserialization will exit with an error.
Zero Copy Deserialization
WARNING: Zero copy deserialization is an experimental feature. It’s recommended to use it only when necessary, i.e., when you have extremely large accounts that cannot be Borsh deserialized without hitting stack or heap limits.
Usage
To enable zero-copy-deserialization, one can pass in the zero_copy
argument to the macro as follows:
#[account(zero_copy)]This can be used to conveniently implement
ZeroCopy so that the account can be used
with AccountLoader.
Other than being more efficient, the most salient benefit this provides is
the ability to define account types larger than the max stack or heap size.
When using borsh, the account has to be copied and deserialized into a new
data structure and thus is constrained by stack and heap limits imposed by
the BPF VM. With zero copy deserialization, all bytes from the account’s
backing RefCell<&mut [u8]> are simply re-interpreted as a reference to
the data structure. No allocations or copies necessary. Hence the ability
to get around stack and heap limitations.
To facilitate this, all fields in an account must be constrained to be
“plain old data”, i.e., they must implement
Pod. Please review the
safety
section before using.
Using zero_copy requires adding the following to your cargo.toml file:
bytemuck = { version = "1.4.0", features = ["derive", "min_const_generics"]}