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Smart ContractsContract ExamplesHello World

⚠️ Disclaimer: This document is provided as a smart contract coding example only. The code has NOT been professionally audited. Use at your own risk - you bear full responsibility for any losses if deployed to production.

Hello World Contract

The simplest possible TAKO smart contract that logs “Hello, TOS!” when called.

Full Source Code

//! Hello World Smart Contract for TAKO
//!
//! This is a minimal example contract that demonstrates logging.
 
#![no_std]
#![no_main]
 
use tako_sdk::*;
 
/// Main contract entrypoint
#[no_mangle]
pub extern "C" fn entrypoint() -> u64 {
    // Log hello message
    log("Hello, TOS!");
 
    // Return success
    SUCCESS
}
 
/// Panic handler (required for no_std)
#[panic_handler]
fn panic(_info: &core::panic::PanicInfo) -> ! {
    loop {}
}

Understanding the Code

Required Attributes

#![no_std]   // No standard library (blockchain environment)
#![no_main]  // No main() function (we use entrypoint)

TAKO contracts run in a constrained environment without access to the standard library or operating system.

SDK Import

use tako_sdk::*;

Imports all TAKO SDK functions including log, SUCCESS, and other utilities.

Entry Point

#[no_mangle]
pub extern "C" fn entrypoint() -> u64 {
    // Contract logic here
    SUCCESS
}
  • #[no_mangle] - Prevents Rust from changing the function name
  • extern "C" - Uses C calling convention for the runtime
  • Returns u64 - 0 for success, non-zero for error

Logging

log("Hello, TOS!");

Logs a message that appears in transaction receipts and can be viewed in explorers.

Panic Handler

#[panic_handler]
fn panic(_info: &core::panic::PanicInfo) -> ! {
    loop {}
}

Required for no_std crates. In production, panics should be avoided - use explicit error returns instead.

Project Setup

Cargo.toml

[package]
name = "hello-world"
version = "0.1.0"
edition = "2021"
 
[lib]
crate-type = ["cdylib"]
 
[dependencies]
tako-sdk = { git = "https://github.com/tos-network/tako" }
 
[profile.release]
opt-level = "z"
lto = true

.cargo/config.toml

[build]
target = "tbpfv3-tos-tos"
 
[target.tbpfv3-tos-tos]
rustflags = [
    "-C", "link-arg=-z", "-C", "link-arg=notext",
]

rust-toolchain.toml

[toolchain]
channel = "1.89.0-dev"

Building

# Build the contract
cargo build --release
 
# The output is at:
# target/tbpfv3-tos-tos/release/hello_world.so

Deploying

# Deploy to testnet
tos_wallet deploy_contract ./hello_world.so
 
# Output:
# Contract deployed at: tos1abc123...

Calling

# Call the contract (no input needed)
tos_wallet call_contract tos1abc123...
 
# Check transaction logs to see "Hello, TOS!"

What’s Next?

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