assert

The assert function is automatically imported into every program from the prelude and it takes an expression which must evaluate to a Boolean. If the Boolean is true then nothing will happen and the code will continue to run otherwise the virtual machine will revert.

Example

Here we have a function which takes two u64 arguments and subtracts them. A u64 cannot be negative therefore the assertion enforces that b must be less than or equal to a.

If the condition is not met, then the virtual machine will revert.

{{#include ../../../code/operations/assertions/src/lib.sw:assert}}