Assertions

An assertion is a condition which must evaluate to the Boolean value of true and its purpose is to prevent undesirable computation when the condition is evaluated to false.

For example, a function may only work if the condition argument < 5 is true. We can use an assertion to enforce this condition by:

• Forcing a revert in the program when 5 <= argument
• Handling the exception with additional code

Handling exceptions may be done through if expressions therefore the following sections will take a look at how we can make the virtual machine revert (safely crash).

• assert: Checks if a condition is true otherwise reverts
• require: Checks if a condition is true otherwise logs a value and reverts
• revert: Reverts the virtual machine with the provided exit code
• assert_eq: Checks if a and b are equal otherwise reverts
• assert_ne: Checks if a and b are not equal otherwise reverts