require

The require 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 rest of the code will continue to run otherwise a log will be emitted and 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 message b is too large will be logged and the virtual machine will revert.

The message is generic therefore it can be any type, in this example it's a string.

{{#include ../../../code/operations/assertions/src/req.sw:require}}