is-eq

Function Signature

(is-eq v1 v2 ...)

• Input: A, A, ...
• Output: bool

Why it matters

The is-eq function is crucial for:

1. Comparing values to check for equality.
2. Implementing conditional logic based on value comparisons.
3. Ensuring data integrity by verifying that values match expected results.
4. Simplifying equality checks in smart contract code.

When to use it

Use is-eq when you need to:

• Compare multiple values for equality.
• Implement logic that depends on whether values are equal.
• Verify that input values match expected constants or variables.
• Simplify equality checks in your contract.

Best Practices

• Ensure all values being compared are of the same type to avoid type errors.
• Use is-eq for simple equality checks and combine with other logical functions for complex conditions.
• Be aware that is-eq does not short-circuit; all values are evaluated.
• Use meaningful variable names for better readability.

Practical Example: Checking User Role

Let's implement a function that checks if a user has a specific role:

(define-constant ADMIN_ROLE "admin")
(define-map UserRoles { userId: principal } { role: (string-ascii 10) })

(define-read-only (is-admin (user principal))
  (let
    (
      (userRole (default-to "none" (map-get? UserRoles { userId: user })))
    )
    (is-eq userRole ADMIN_ROLE)
  )
)

;; Usage
(map-set UserRoles { userId: tx-sender } { role: "admin" })
(is-admin tx-sender) ;; Returns true

This example demonstrates:

1. Using is-eq to compare a user's role with the constant ADMIN_ROLE.
2. Handling the case where the user role is not set by providing a default value.
3. Implementing a read-only function to check if a user is an admin.

Common Pitfalls

1. Comparing values of different types, leading to type errors.
2. Assuming is-eq short-circuits like and or or (it does not).
3. Using is-eq for complex conditions where other logical functions might be more appropriate.
4. Not handling cases where values might be none or unset.

Related Functions

• is-some: Checks if an optional value is some.
• is-none: Checks if an optional value is none.
• asserts!: Asserts a condition and throws an error if it is false.

Conclusion

The is-eq function is a fundamental tool for comparing values in Clarity smart contracts. It provides a straightforward way to check for equality, enabling developers to implement conditional logic and verify data integrity. When used effectively, is-eq simplifies equality checks and enhances the readability and maintainability of your smart contract code.