ExpectPrecondition

Type

statement

Summary

Check a precondition

Syntax

expect [that] <Condition>

Description

Use this statement at the start of a handler to check that necessary preconditions for the handler are satisfied. For example, the handler may require that its parameters have a particular structure or fall within a particular range, or may need the system to be in a specific state.

Note that if the Condition is false, this statement will throw an error with the slightly-unhelpful message that "assertion failed". Usually, it will be more useful to use ExpectsPreconditionWithReason instead.

Examples

handler BoxValue(in pValue as any) returns Array
	return { "__VALUE": pValue }
end handler

handler UnBoxValue(in pBox as Array) returns any
	expect that "__VALUE" is among the elements of pBox
	return pBox["__VALUE"]
end handler

Related

statement: ExpectPreconditionWithReason