Clarity Control flow & error handling - asserts!

Clarity of Mind book discusses control flow and error handling. Here’s an example of how it looks like to refactor from if statements to asserts!.

In the book, Marvin Janssen starts with a function called is-valid-caller, discussed in the chapter on private functions.

In that chapter, there’s an if function to only allow the action (add/delete a recipient) if the tx-sender is equal to the principal that deployed the contract:

(define-public (add-recipient (recipient principal) (amount uint))
    (if (is-valid-caller)
        (ok (map-set recipients recipient amount))
        err-invalid-caller
    )
)
(define-public (delete-recipient (recipient principal))
    (if (is-valid-caller)
        (ok (map-delete recipients recipient))
        err-invalid-caller
    )
)

Then, in the asserts! chapter the code has been refactored to use asserts! instead of if.

Putting those two pieces in a git repository, you can see a diff highlighting the refactored part, from if to asserts!:

@@ -11,20 +11,22 @@
 (define-private (is-valid-caller)
     (is-eq contract-owner tx-sender)
 )

 (define-public (add-recipient (recipient principal) (amount uint))
-    (if (is-valid-caller)
+    (begin
+        ;; Assert the tx-sender is valid.
+        (asserts! (is-valid-caller) err-invalid-caller)
         (ok (map-set recipients recipient amount))
-        err-invalid-caller
     )
 )

 (define-public (delete-recipient (recipient principal))
-    (if (is-valid-caller)
+    (begin
+        ;; Assert the tx-sender is valid.
+        (asserts! (is-valid-caller) err-invalid-caller)
         (ok (map-delete recipients recipient))
-        err-invalid-caller
     )
 )

 ;; Two example calls to the public functions:
 (print (add-recipient 'ST1J4G6RR643BCG8G8SR6M2D9Z9KXT2NJDRK3FBTK u500))

Hope this helps the readers of the book to visualize the actual change.