Modules

There are two types of smart contracts in dfinance: module and script.

Difference between them that module is published into blockchain storage and is stored under the publisher account, while script is simply a transaction-as-script and can only operate with existing modules.

The Move Book also has a section about modules in Move language.

Write a module

Let's see an example of a small module that will just add two numbers (a and b):

module Math {
    public fun add(a: u64, b: u64): u64 {
        a + b
    }
}

Let's compile this module using dncli. Compiler requires sender's address as it's included into bytecode. This address will then be verified on module publish.

dncli q vm compile <path-to-mvir> <address> --to-file <output file>

Replace variables in this pattern with your own and you will get a compiled module in the specified output file. When it's done, you can publish your module:

dncli tx vm publish <output file> --from <account>

Check your transaction by querying its id, which was returned in the output.

dncli q tx <id>

If you see a contract_status event, with status keep inside, everything published fine!

When it's done your module is be published under your address, and you and other users can access it in their modules or scripts:

use {{address}}::Math;

Just replace {{address}} with yours and you can use this module.