Ghost fields for Contract Programming

[bearophile]

Tomek S.:

> You can do:
> 
> class C {
>   version(unittest) int temp;
>   invariant() {
>     // use temp
>   }
> }
> 
> Or am I missing something?

D2 has several ways to perform conditional compilation, so you may implement hand-made ghost fields using a version(debug). And ghost fields are very important to start with (I was not sure to submit an enhancement request).

There are two things that maybe you are missing. A field like:

version(unittest) int temp;

gets compiled when you use the -unittest, and gets removed otherwise. While the presence of ghost fields is determined by the presence of active contracts, that currently are run with the code is compiled in non-release build (so they are not related to the -unittest switch).

The second problem is that inside a method foo() of that class C you may write:

    void foo() {
        version(unittest) temp++;
    }

But well implemented ghost fields are never visible inside the body of methods. So if you try to use them inside foo() the compiler has to raise a compile error.

Bye,
bearophile