const?? When and why? This is ugly!

[grauzone]

Walter Bright wrote:
> Derek Parnell wrote:
>> import std.stdio;
>> void main()
>> {
>>   int [] a = new int [1];
>>
>>    a [0] = 1;
>>
>>    invariant (int) [] b = cast (invariant (int) []) a;
>>
>>    writef ("a=%s b=%s\n", a [0], b[0]);
>>    a [0] += b [0];
>>    writef ("a=%s b=%s\n", a [0], b[0]);
>>    a [0] += b [0];
>>    writef ("a=%s b=%s\n", a [0], b[0]);
>> }
>>    The problem is that we have declared 'b' as invariant, but the 
>> program is
>> allowed to change it. That is the issue.
>>
> 
> The following also compiles:
> 
> char c;
> int* p = cast(int*)&c;
> *p = 5;
> 
> and is clearly buggy code. Whenever you use a cast, the onus is on the 
> programmer to know what they are doing. The cast is an escape from the 
> typing system.

Sometimes a cast can break a program, sometimes a cast is absolutely 
harmless:

int w, h;
double ratio = (cast(double)w) / h;

Sure you don't want to introduce something like dangerous_cast() if a 
cast dangerous, because it e.g. reinterprets raw memory bytes, or 
aliases immutable memory to mutable memory?