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
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