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compose-capability

Use compose-capability to compose and grant capabilities in a nested structure to control the scope of how the capabilities are applied. By convention, capabilities are defined using all uppercase letters.

With this function, you can define the specified CAPABILITY within the context of an outer defcap declaration. The function is only valid within the distinct defcap body of its outer capability, such that the CAPABILITY you specify for the compose-capability function is included when you call the with-capability function for its outer capability.

For example, if you call (with-capability (OUTER-CAP) OUTER-BODY) and the OUTER-CAP declaration includes the (compose-capability (INNER-CAP)) function, the INNER-CAP capability is granted in the scope of the OUTER-BODY logic.

Basic syntax​

To compose and grant a specified CAPABILITY within an outer capability body, use the following syntax:

(compose-capability CAPABILITY)

Arguments​

Use the following argument to specify the CAPABILITY for the compose-capability Pact function.

ArgumentTypeDescription
CAPABILITYcapabilitySpecifies the capability to include in the scope of an outer capability.

Return value​

The compose-capability function returns a boolean value to indicate success or failure in requesting the grant of the specified CAPABILITY.

Examples​

The following example demonstrates how to use the compose-capability function within the body of the TRANSFER capability and include the DEBIT and CREDIT capabilities when the with-capability function is called:

(defcap TRANSFER:bool
    ( id:string
      sender:string
      receiver:string
      amount:decimal
    )
    @managed amount TRANSFER-mgr
    (enforce-unit id amount)
    (enforce (> amount 0.0) "Amount must be positive")
    (compose-capability (DEBIT id sender))
    (compose-capability (CREDIT id receiver))
)
...
    (with-capability (TRANSFER id sender receiver amount)
     ...
    )