Create PDA with no data in it

Question

I want to create PDA with no data in it, only SOL balance is needed. Reading following questions (q1, q2) I found out that I need to create System Account PDA, but I am having trouble to implement this with anchor. Some small example how to create and use it would be appreciated.

There are some question that comes using System Account PDA:

• In instruction context, System Account PDA should be specified as SystemAccount?
• Would program be able to withdraw SOL from System Account PDA and ensure that the program is the only account that withdraw SOL?
• When calling the transaction that withdraw SOL from System Account PDA, signers are not required since it's PDA and there is no private key?

Answer 1

You can create a PDA with an empty account struct. For example

pub struct Example<'info> {
    #[account(
        init,
        seeds = [..],
        bump,
        payer = ..,
        space = 8,
    )]
    empty_pda: Account<'info, Empty>  
}
#[account]
pub struct Empty {}

1. No. An Account<'info> is what you should use.
2. Yes a program will be able to withdraw sol from the PDA. By default, making the PDA a program account(as is done above) ensures that only the program can sign withdrawals from that PDA.
3. Correct, signers are not required for a PDA in the client-side because PDAs have no private key and it's impossible for them to sign that way. Here's a link that shows how to withdraw sol from a PDA.