Managing Space in the Zero Account

Question

I am looking to use zero account (Anchor) for the first time in my program. I have read the example and from the look of it, it doesn't require the space constraint like init does. I wanted to use a vector field in my struct whose initial length will be zero but will increase eventually. How do I let the program know how much space should it reserve for the vector without space constraint?

Answer 1

You can initialize it like this:

    #[account(init, payer=payer, space = 40 , seeds = [b"seeds".as_ref()], bump)]
    account_pda: Account<'info, AccountStruct>

#[account]
#[derive(Default)]
pub struct AccountStruct{
    pub addresses: Vec<Pubkey>,
    pub bump: u8,
}

impl AccountStruct{
    pub fn space(len: usize) -> usize {
        8 + (4 + ((len + 1) * 32)) + 1
    }
}

Then use like this. I realloc 32 bytes each time because I add a new Pubkey to the Vec, which uses 32 bytes.

    #[account(mut, seeds = [b"seeds".as_ref()], bump = account_pda.bump,
    realloc = AccountStruct::space(account_pda.addresses.len() as usize) , realloc::payer = payer, realloc::zero = false,)]
    account_pda: Account<'info, AccountStruct>,

Hope it helps.