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The Adder SC

The Adder smart contract is a simple smart contract with an add functionality and a global variable that can be incremented.

/// One of the simplest smart contracts possible,
/// it holds a single variable in storage, which anyone can increment.
#[multiversx_sc::contract]
pub trait Adder {
    #[view(getSum)]
    #[storage_mapper("sum")]
    fn sum(&self) -> SingleValueMapper<BigUint>;

    #[init]
    fn init(&self, initial_value: BigUint) {
        self.sum().set(initial_value);
    }

    #[upgrade]
    fn upgrade(&self, initial_value: BigUint) {
        self.init(initial_value);
    }

    /// Add desired amount to the storage variable.
    #[endpoint]
    fn add(&self, value: BigUint) {
        self.sum().update(|sum| *sum += value);
    }
}

We notice 4 functions:

  • sum - this is a global variable, a SingleValueMapper (a single value) of type BigUint (unsigned integer);
  • init - the constructor;
  • add - function that increments the global variable (sum) with the value parameter;
  • upgrade - function executed when upgrading the contract.

We notice 5 types of annotations:

  • #[view(getSum)] - this is a function that allows you to read the storage variable by calling the function getSum;
  • #[storage_mapper("sum")] - this is a global variable (also called a storage) stored at the contract address;
  • #[init] - the constructor function; this is called when deploying the contract;
  • #[upgrade] - this function is called when upgrading the contract;
  • #[endpoint] - an endpoint is a function callable directly by the user; A function not having this annotation will not be exposed publicly.

Here is the smart contract code listed above and here are all the files needed for compilation.

Let's compile the contract:

costin@Byblos:~/mvx/mx-contracts-rs/contracts/adder$ sc-meta all build
 /home/costin/mvx/mx-contracts-rs/contracts/adder

Found 1 contract crates.

(1/1)
In /home/costin/mvx/mx-contracts-rs/contracts/adder/meta
Calling `cargo run build`
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.05s
     Running `/home/costin/mvx/mx-contracts-rs/target/debug/adder-meta build`
Using workspace target directory: /home/costin/mvx/mx-contracts-rs/target ...
Building adder.wasm in /home/costin/mvx/mx-contracts-rs/contracts/adder/wasm ...
RUSTFLAGS="-C link-arg=-s -C link-arg=-zstack-size=131072" cargo build --target=wasm32-unknown-unknown --release --target-dir /home/costin/mvx/mx-contracts-rs/target
   Compiling proc-macro2 v1.0.86
   Compiling unicode-ident v1.0.13
   Compiling smallvec v1.13.2
   Compiling autocfg v1.4.0
   Compiling hex v0.4.3
   Compiling endian-type v0.1.2
   Compiling arrayvec v0.7.6
   Compiling unwrap-infallible v0.1.5
   Compiling bitflags v2.6.0
   Compiling hex-literal v0.4.1
   Compiling nibble_vec v0.1.0
   Compiling radix_trie v0.2.1
   Compiling num-traits v0.2.19
   Compiling quote v1.0.37
   Compiling syn v2.0.77
   Compiling multiversx-sc-codec-derive v0.21.0
   Compiling multiversx-sc-derive v0.53.2
   Compiling multiversx-sc-codec v0.21.0
   Compiling multiversx-sc v0.53.2
   Compiling adder v0.0.0 (/home/costin/mvx/mx-contracts-rs/contracts/adder)
   Compiling multiversx-sc-wasm-adapter v0.53.2
   Compiling adder-wasm v0.0.0 (/home/costin/mvx/mx-contracts-rs/contracts/adder/wasm)
    Finished `release` profile [optimized] target(s) in 8.69s
Copying /home/costin/mvx/mx-contracts-rs/target/wasm32-unknown-unknown/release/adder_wasm.wasm to ../output/adder.wasm ...
Calling wasm-opt on ../output/adder.wasm ...
Extracting imports to ../output/adder.imports.json ...
Checking EI version: 1.3 ... OK
Packing ../output/adder.mxsc.json ...
Contract size: 696 bytes.

Let's check the contract:

costin@Byblos:~/mvx/mx-contracts-rs/contracts/adder$ ls -l output/
total 16
-rw-rw-r-- 1 costin costin 1792 nov  7 13:28 adder.abi.json
-rw-rw-r-- 1 costin costin  262 nov  7 13:28 adder.imports.json
-rw-rw-r-- 1 costin costin 4070 nov  7 13:28 adder.mxsc.json
-rwxrwxr-x 1 costin costin  696 nov  7 13:28 adder.wasm

We notice that the resulted contract (adder.wasm) has 696 bytes.

Practice​

  • Compile the Adder contract.