Struct Vector 

pub struct Vector<T>
where
    T: Storable,
{ /* private fields */ }

Vector is a contract-level data structure to provide abstraction by utilizing Get and Set operations associated with Contract Storage. It supports lazy read/write on elements that can be iterated.

Vector

Vector can be a Contract Field defined in the contract struct. E.g.

#[contract]
struct MyContract {
    vector: Vector<u64> // this vector declares to store u64 integers to world state
}

The value can be obtained by indexing operations. E.g.

let data = self.vector[0]; // can be either a read from cached value or a read from world state 
self.vector[0] = data; // No actual write to world state at this line

Iteration

Iteration may involve read from world state. E.g.

// Iterate over immutable reference to the data
self.vector.iter().for_each(|item|{
    ...
});
 
// Iterate over mutable reference to the data
self.vector.iter_mut().for_each(|item|{
    //...
});

Storage Model

Account Storage State Key Format:

Component	Key	Value (Data type)
Length	P, 0	u32
Element	P, 1, I	user defined data (borsh-serialized)

• P: parent key
• I: little endian bytes of index (u32)

Lazy Write

Trait Storage implements the Vector so that data can be saved to world state

1. after execution of action method with receiver &mut self; or
2. explicitly calling the setter Self::set().

Implementations

impl<'a, T> Vector<T>

where T: Storable + Clone,

pub fn new() -> Self

pub fn len(&self) -> usize

length of the vector

pub fn is_empty(&self) -> bool

check if it is empty vector

pub fn push(&mut self, value: &T)

push adds item to the last of vector, which does not immediately take effect in Contract Storage.

pub fn pop(&mut self)

pop removes the last item in the vector, which does not immediately take effect in Contract Storage. Pop doest not return the poped item for saving reading cost.

pub fn iter(&'a self) -> VectorIter<'a, T>

iter returns VectorIter which implements Iterator

pub fn iter_mut(&'a mut self) -> VectorIterMut<'a, T>

iter_mut returns VectorIterMut which implements Iterator

Trait Implementations

impl<T> Clone for Vector<T>

where T: Storable + Clone,

fn clone(&self) -> Vector<T>

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T> Default for Vector<T>

where T: Storable + Default,

fn default() -> Vector<T>

Returns the “default value” for a type.

impl<T> Index<usize> for Vector<T>

where T: Storable + Clone,

type Output = T

The returned type after indexing.

fn index(&self, index: usize) -> &Self::Output

Performs the indexing (container[index]) operation.

impl<T> IndexMut<usize> for Vector<T>

where T: Storable + Clone,

fn index_mut(&mut self, index: usize) -> &mut Self::Output

Performs the mutable indexing (container[index]) operation.

impl<T> Storable for Vector<T>

where T: Storable + Clone,

fn __load_storage(field: &StoragePath) -> Self

the implementation should eventually call get() to obtain data from world-state and assign the value to the fields of struct

fn __save_storage(&mut self, field: &StoragePath)

the implementation should eventually call set() to obtain fields’ value of struct and save it to world-state