Remote type

Your contract may rely on communication with another one. For example, it could instantiate a CW20 contract and, during the workflow, send Mint messages to it. If CW20 contract was created using sylvia, it would have a Remote type generated which would make this process more user friendly. It is possible to send queries and build execute messages by using Remote.

To check some examples, checkout the sylvia repository and go to sylvia/tests/remote.rs and sylvia/tests/executor.rs.

Working with Remote

Remote represents some contract instantiated on the blockchain. It aims to give contract developers a gateway to communicate with other contracts. It has only one field, which is a remote contract address. There are two main methods implemented for this type:

• querier, which returns a BoundQuerier type,
• executor that returns an ExecutorBuilder type.

BoundQuerier implements Querier traits of every sylvia contract and interface. Querier traits are auto-generated by contract and interface macros and consist of every query method of the given contract and interface.

Similar to BoundQuerier and Querier, the ExecutorBuilder implements every Executor trait auto-generated for sylvia contracts and interfaces. Executor traits contain exec methods.

If we create a contract relying on our CounterContract, it could query its state as below.

use sylvia::types::Remote;
use crate::whitelist::sv::Querier as WhitelistQuerier;
use crate::contract::sv::Querier as ContractQuerier;

let count = Remote::<CounterContract>::new(addr)
    .querier(&ctx.deps.querier)
    .count()?
    .count;

let admins = Remote::<CounterContract>::new(ctx.info.sender)
    .querier(&ctx.deps.querier)
    .admins()?;

Important to note is that Remote is generic over the contract type. To use it in context of some contract, just initialize it generic over it.

In case of contract initializing the CW20 contract you might want to keep its address in the state.

use sylvia::types::Remote;

struct Contract<'a> {
    cw20: Item<Remote<'a, Cw20Contract>>,
}

Then to query the contract load the remote, call querier on it which will return BoundQuerier and then call the query method on it.

self.cw20
    .load(ctx.deps.storage)?
    .querier(&ctx.deps.querier)
    .query_all_balances()?

Let's see an example for an exec method call:

use sylvia::types::Remote;
use crate::contract::sv::Executor;

let increment_msg: WasmMsg = Remote::<CounterContract>::new(addr)
    .executor()
    .increment_count()?
    .build();

Next step

Phew.. that was a journey. We learned most of the sylvia features and should be ready to create our first contracts. In the last chapter, we will learn about some of the best practices that will make our code more readable and maintainable.