Signatories and Observers

-- SignatoriesAndObservers.daml
module SignatoriesAndObservers where


-- ── Single signatory ────────────────────────────────────
-- Only the bank must authorize creation.
-- The client observes (sees the contract) but is not a signer.
template BankDeposit
  with
    bank   : Party
    client : Party
    amount : Decimal
  where
    signatory bank
    observer  client
    ensure amount > 0.0


-- ── Multiple signatories ─────────────────────────────────
-- Both parties must authorize the contract.
-- This means NEITHER can create or archive it without the other.
-- Comma-separated on one line, or use the `signatory` keyword twice.
template BilateralAgreement
  with
    partyA : Party
    partyB : Party
    terms  : Text
  where
    signatory partyA, partyB


-- ── List of observers ───────────────────────────────────
-- The observer field can be a list of parties.
template Announcement
  with
    issuer    : Party
    audience  : [Party]
    message   : Text
  where
    signatory issuer
    observer  audience


-- ── Computed signatories ─────────────────────────────────
-- Signatories are expressions evaluated at runtime.
-- Any party in the `with` block can be used.
template ConditionalAuth
  with
    primary   : Party
    secondary : Party
    amount    : Decimal
  where
    -- If amount exceeds threshold, require both to sign.
    signatory if amount > 10000.0 then [primary, secondary] else [primary]
    observer  secondary
    ensure amount > 0.0

Key points

Signatories

• All signatories must authorize the transaction that creates or archives the contract.
• Signatories are expressions: they can be a single Party, a list [Party], a conditional, or any expression of type Party or [Party].
• There must be at least one signatory. An empty signatory list is a compile-time error.

Observers

• A party in the observer field can see the contract but cannot authorize actions or create choices using that contract's authority.

Stakeholder rules

• Signatories are automatically observers: you do not need to list them twice.
• The controller of a choice must be an observer or signatory of the contract; otherwise they cannot see it to exercise it.