D supports contract programming, which can help you ensure an object's state is always valid and object methods are passed with correct parameters and returns valid values, including while using class inheritance. Here, we'll see how to use these features and why they work the way they do.
Perform the following steps:
When writing an
interface,class, orstruct, addinandoutblocks to methods, right after the signatures, and also addinvariantblocks to the aggregate.Put assertions in the
inblocks to verify your preconditions.Put assertions in the
outblocks to verify your postconditions. Theoutblock may take an argument to access the method's return value.Add the
bodykeyword before your method's body but after itsinandoutblocks (if it has them).In child classes, also use
incontracts to reassert your input requirements, even if they are the same as the parent class.Put assertions in the
invariantblocks to verify...