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.
Preparation#
Compiling concordium-std
without the std
feature requires using the rust
nightly toolchain, which can be installed using rustup
:
$rustup toolchain install nightly
Then add the wasm32 target by using
$rustup +nightly target add wasm32-unknown-unknown
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.
You can update your Cargo.toml file by using:
[dependencies]
concordium-std = { version = "6.0", default-features = false }
Note
To compile your smart contracts, a memory allocator is used.
concordium-std
version <6.0.0
hard-coded the use of the wee_alloc allocator.
In concordium-std
version >=6.0.0
, wee_alloc
is a feature and needs to be explicitly enabled.
When std
feature is enabled, the allocator provided by the Rust standard library is used
by default but when the wee_alloc
feature is enabled in addition, wee_alloc is used instead.
You can enable the std
feature and the wee_alloc
feature in concordium-std
version >=6.0.0
by using:
[dependencies]
concordium-std = {version = "6.0", features = ["wee_alloc"]}
Alternatively, if you want to test with and without wee_alloc
enabled add a wee_alloc
feature to the smart contract crate as follows:
[features]
default = ["std", "wee_alloc"]
std = ["concordium-std/std"]
wee_alloc = ["concordium-std/wee_alloc"]
The above code blocks will use the wee_alloc allocator and not the allocator provided by the Rust standard library when compiled with the default features as follows:
$cargo concordium build
When no_std
is used either wee_alloc
must be enabled, or another global allocator
must be set in the smart contract. You can add the wee_alloc
feature by using:
[features]
wee_alloc = ["concordium-std/wee_alloc"]
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
:
[features]
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 --features wee_alloc
Note
The above command works with concordium-std
version >=6.0.0
, because the
wee_alloc
feature needs to be explicitly enabled.
If you use concordium-std
version <6.0.0
use the following instead:
$cargo +nightly concordium build -- --no-default-features