Good design patterns

Patterns have been useful in the programming world, as both a source of design inspiration, and a document of good design practices. This document is a catalog of DAML patterns intended to provide the same facility in the DA/DAML application world.

You can checkout the examples locally via daml new daml-patterns --template daml-patterns.

Initiate and Accept

The Initiate and Accept pattern demonstrates how to start a bilateral workflow. One party initiates by creating a proposal or an invite contract. This gives another party the chance to accept, reject or renegotiate.

Multiple party agreement

The Multiple Party Agreement pattern uses a Pending contract as a wrapper for the Agreement contract. Any one of the signatory parties can kick off the workflow by creating a Pending contract on the ledger, filling in themselves in all the signatory fields. The Agreement contract is not created on the ledger until all parties have agreed to the Pending contract, and replaced the initiator’s signature with their own.

Delegation

The Delegation pattern gives one party the right to exercise a choice on behalf of another party. The agent can control a contract on the ledger without the principal explicitly committing the action.

Authorization

The Authorization pattern demonstrates how to make sure a controlling party is authorized before they take certain actions.

Locking

The Locking pattern exhibits how to achieve locking safely and efficiently in DAML. Only the specified locking party can lock the asset through an active and authorized action. When a contract is locked, some or all choices specified on that contract may not be exercised.