Why I chose D over Ada and Eiffel

[John Colvin]

On Thursday, 29 August 2013 at 13:33:52 UTC, Gour wrote:
> On Sun, 25 Aug 2013 17:06:27 +0200
> "bearophile" <bearophileHUGS at lycos.com> wrote:
>
>> Probably working even more you can make the D entry a bit more
>> statically safe (eventually you could reach the level of Ada 
>> code) but
>> the amount of work and code becomes excessive, and the 
>> resulting D
>> code becomes unnatural, and rather not idiomatic.
>
> Still considering whether to focus on Ada or D for my project, 
> I wonder
> if D can do stuff like (from wikipedia page):
>
> type Day_type   is range    1 ..   31;
> type Month_type is range    1 ..   12;
> type Year_type  is range 1800 .. 2100;
> type Hours is mod 24;
> type Weekday is (Monday, Tuesday, Wednesday, Thursday, Friday, 
> Saturday, Sunday);
> 
> type Date is
>    record
>      Day   : Day_type;
>      Month : Month_type;
>      Year  : Year_type;
>    end record;
>
> subtype Working_Hours is Hours range 0 .. 12;
> subtype Working_Day is Weekday range Monday .. Friday;
> 
> Work_Load: constant array(Working_Day) of Working_Hours
>    := (Friday => 6, Monday => 4, others => 10);
>
>
> and ensure type-safety for such custom types?
>
>
> Sincerely,
> Gour

just something I whipped up in a few mins:
import std.typecons;
import std.exception;

struct Limited(T, T lower, T upper)
{
	T _t;
	mixin Proxy!_t; //Limited acts as T (almost)
	invariant()
	{
		enforce(_t >= lower && _t <= upper);
	}
	this(T t)
	{
		_t = t;
	}
}

auto limited(T, T lower, T upper)(T init = T.init)
{
	return Limited!(T, lower, upper)(init);
}

unittest
{
	enum l = [-4,9];
	auto a = limited!(int, l[0], l[1])();
	foreach(i; l[0] .. l[1]+1)
	{
		a = i;
	}
	
	assertThrown({a = -5;}());
	assertThrown({a = 10;}());
}


This could be a lot more generic than it is. Redesigning 
Restricted to hold a pointer to a function that does the check 
would be one way.