Build using no_std

This guide shows how to enable no_std for your rust smart contract, potentially reducing the size of the resulting Wasm module by several kilobytes.


Compiling concordium-std without the std feature requires using the rust nightly toolchain, which can be installed using rustup:

$rustup toolchain install nightly

Setting up the module for no_std

The concordium-std library exposes a std feature, which enables the use of the rust standard library. This feature is enabled by default.

To disable it, one must simply disable default features for the concordium-std in the dependencies of your module.

concordium-std = { version: "=0.2", default-features = false }

To be able to toggle between with and without std, also add a std to your own module, which enables the std feature of concordium-std:

std = ["concordium-std/std"]

This is the setup of the smart contract examples, where std for each smart contract module is enabled by default.

Building the module

In order to use the nightly toolchain, add +nightly right after cargo:

$cargo +nightly concordium build

If you want to disable the default features of your own smart contract module, you can pass extra arguments for cargo:

$cargo +nightly concordium build -- --no-default-features