Implicit integer casting

[Manu]

On 18 March 2012 21:15, Tove <tove at fransson.se> wrote:

> On Sunday, 18 March 2012 at 19:08:54 UTC, Manu wrote:
>
>> So D is really finicky with integer casts. Basically everything that might
>> produce a loss of data warning in C is an outright compile error.
>> This results in a lot of explicit casting.
>>
>> Now I don't take issue with this, actually I think it's awesome, but I
>> think there's one very important usability feature missing from the
>> compiler with such strict casting rules...
>> Does the compiler currently track the range of a value, if it is known?
>> And
>> if it is known, can the compiler stop complaining about down casts and
>> perform the cast silently when it knows the range of values is safe.
>>
>> int x = 123456;
>> x &= 0xFF; // x is now in range 0..255; now fits in a ubyte
>> ubyte y = x; // assign silently, cast can safely be implicit
>>
>> I have about 200 lines of code that would be so much more readable if this
>> were supported.
>> I'm finding that in this code I'm writing, casts are taking up more space
>> on many lines than the actual term being assigned. They are really getting
>> in the way and obscuring the readability.
>> Not only masks, comparisons are also often used of limit the range of
>> values. Add D's contracts, there is good chance the compiler will have
>> fairly rich information about the range of integers, and it should
>> consider
>> that while performing casts.
>>
>
> Walter even wrote an article about it:
> http://drdobbs.com/blogs/**tools/229300211<http://drdobbs.com/blogs/tools/229300211>


Interesting. This article claims: Can we do better? Yes, with "Value Range
Propagation", a historically obscure compiler optimization that became a
handy feature in the D programming language.

But it doesn't seem to work. Am I just doing something wrong?
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