Compile time opAssign/@property constraints

[Stefan Koch]

On Friday, 4 January 2019 at 11:45:24 UTC, Jacob Shtokolov wrote:
> On Friday, 4 January 2019 at 10:34:07 UTC, Basile.B wrote:
>> Show us some code.
>
> Here is the simple example:
>
> https://run.dlang.io/gist/1a06dd703bea5548ee72b4713a7ce5f6
>
> The thing I'm trying to do is to make an experimental port (for 
> education purposes) of https://github.com/fthomas/refined 
> library for Scala, which allows to set constraints on basic 
> types like numeric, bool, string, etc.
>
> For example, you can force an integer variable to take a range 
> between 0 and 15. And if constraint is not satisfied, you get a 
> compile time error.
>
> There is no predicate in my example, but even if I add one 
> (using alias template parameter), it shows the same error.
>
> So is that possible in D?

You have'd to use a template to "construct" your variables;
struct ConstrainedInt
{
   int val;
   alias val this;
}

template makeConstrainedInt(int Value)
{
     static assert(Value <= 15 && Value >= 0);
     enum makeConstrainedInt = ConstrainedInt(Value);
}


However this relies on your virtue not to call constraintInt 
constructor directly.
and always use the template.