sol-transfer.rs

fn transfer_from_account_we_own(
    src: &mut AccountInfo, // we better own this account though
    dst: &mut AccountInfo,
    amount: u64,
) -> ProgramResult {
    **src.try_borrow_mut_lamports()? = src
        .lamports()
        .checked_sub(amount)
        .ok_or(ProgramError::InvalidArgument)?;
    **dst.try_borrow_mut_lamports()? = dst
        .lamports()
        .checked_add(amount)
        .ok_or(ProgramError::InvalidArgument)?;
    Ok(())
}