Rust for Web3
Starter Pack

// Transfer SOL from one account to another — ownership moves
pub fn transfer_sol(
    ctx: Context<TransferSol>,
    amount: u64,
) -> Result<()> {
    let from = &mut ctx.accounts.from;  // borrow mut
    let to = &mut ctx.accounts.to;    // borrow mut
    **from.try_borrow_mut_lamports()? -= amount;
    **to.try_borrow_mut_lamports()? += amount;
    Ok(())
}

// Solana account data layout using Borsh
#[derive(BorshSerialize, BorshDeserialize, Debug)]
pub struct TaskAccount {
    pub discriminator: [u8; 8],  // anchor discriminator
    pub author: Pubkey,
    pub title: String,
    pub completed: bool,
    pub created_at: i64,
}

// Anchor error codes with #[msg]
#[error_code]
pub enum TaskError {
    #[msg("Task is already completed")]
    AlreadyCompleted,
    #[msg("Deadline has passed")]
    DeadlinePassed,
    #[msg("Unauthorized: not the task author")]
    Unauthorized,
}

// Anchor program for a simple counter
#[program]
pub mod counter {
    use super::*;

    #[instruction]
    pub fn increment(ctx: Context<Increment>) -> Result<()> {
        ctx.accounts.counter.count += 1;
        Ok(())
    }

    #[derive(Accounts)]
    pub struct Increment<'info> {
        #[account(mut, seeds = [b"counter", user.key().as_ref()], bump)]
        pub counter: Account<'info, Counter>,
        #[account(mut)]
        pub user: Signer<'info>,
    }
}

// Cross-program invocation without Anchor
pub fn invoke_transfer(
    from: &AccountInfo,
    to: &AccountInfo,
    amount: u64,
) -> Result<()> {
    let ix = Instruction {
        program_id: solana_program::system_program::ID,
        accounts: vec![
            AccountMeta::new(from.key(), true),
            AccountMeta::new(to.key(), false),
        ],
        data: solana_program::system_instruction::transfer(&from.key(), &to.key(), amount).data,
    };
    solana_program::program::invoke(&ix, &[from.clone(), to.clone()])
}