Rant after trying Rust a bit

[vitus via Digitalmars-d]

On Friday, 24 July 2015 at 04:42:59 UTC, Walter Bright wrote:
> On 7/23/2015 3:12 PM, Dicebot wrote:
>> On Thursday, 23 July 2015 at 22:10:11 UTC, H. S. Teoh wrote:
>>> OK, I jumped into the middle of this discussion so probably 
>>> I'm speaking
>>> totally out of context...
>>
>> This is exactly one major advantage of Rust traits I have been 
>> trying to
>> explain, thanks for putting it up in much more understandable 
>> way :)
>
> Consider the following:
>
>     int foo(T: hasPrefix)(T t) {
>        t.prefix();    // ok
>        bar(t);        // error, hasColor was not specified for T
>     }
>
>     void bar(T: hasColor)(T t) {
>        t.color();
>     }
>
> Now consider a deeply nested chain of function calls like this. 
> At the bottom, one adds a call to 'color', and now every 
> function in the chain has to add 'hasColor' even though it has 
> nothing to do with the logic in that function. This is the pit 
> that Exception Specifications fell into.
>
> I can see these possibilities:
>
> 1. Require adding the constraint annotations all the way up the 
> call tree. I believe that this will not only become highly 
> annoying, it might make generic code impractical to write 
> (consider if bar was passed as an alias).
>
> 2. Do the checking only for 1 level, i.e. don't consider what 
> bar() requires. This winds up just pulling the teeth of the 
> point of the constraint annotations.
>
> 3. Do inference of the constraints. I think that is 
> indistinguishable from not having annotations as being 
> exclusive.
>
>

Fun begins:

	void foo(T)(T t)
	if(hasPrefix!T || hasSuffix!T){
		static if(...)t.prefix();
		else t.suffix();

		mixin("t.bar();");
	}