Array types not treated uniformly when passed as ranges

[spir]

On 02/15/2011 03:00 PM, Steven Schveighoffer wrote:
> On Mon, 14 Feb 2011 21:18:39 -0500, jam <gr0v3er at gmail.com> wrote:
>
>> Hi all,
>>
>> Just curious as to the difference in the built-in variable length
>> array vs. the std.container.Array and fixed length arrays when it
>> comes to using them in functions that take Ranges.
>>
>> For instance the following does not compile:
>>
>> import std.algorithm;
>> import std.stdio;
>> import std.range;
>> import std.conv;
>> import std.container;
>> import std.array;
>>
>> void main() {
>>
>> int[5] builtin_fixed;
>> int[] builtin_variable;
>> Array!(int) con_array;
>>
>> con_array.length(5);
>> builtin_variable.length = 5;
>>
>> fill(builtin_variable, 9); //ok, no error
>> isSorted(builtin_variable); //ditto
>>
>> //The following 4 statements produce errors
>> fill(builtin_fixed, 9);
>> fill(con_array, 9);
>>
>> isSorted(con_array);
>> isSorted(builtin_fixed);
>>
>> }
>>
>> The errors are variations on:
>>
>> Error: template std.algorithm.fill(Range,Value) if
>> (isForwardRange!(Range) && is(typeof(range.front = filler))) does not
>> match any function template declaration
>> Error: template std.algorithm.fill(Range,Value) if
>> (isForwardRange!(Range) && is(typeof(range.front = filler))) cannot
>> deduce template function from argument types !()(int[5LU],int)
>>
>> If I change those 4 statements to:
>>
>> fill(builtin_fixed[], 9);
>> fill(con_array[], 9);
>>
>> isSorted(con_array[]);
>> isSorted(builtin_fixed[]);
>>
>> effectively passing ranges (std.container.Array!(int).Array.Range in
>> the case of con_array, and int[] for builtin_fixed) which then works
>> as expected. This all makes sense, and it's easy enough to write
>> wrappers, but I would (well and I did) expect the first way to just
>> work. This may just be a nitpick I guess, but being new to the
>> language this little detour involved quite a bit of time research (not
>> a bad thing, I did learn quite a bit in the process), but makes me
>> wonder if I am missing something fundamental regarding when I should
>> be using these different array types.
>
> This is because:
>
> 1. a fixed-sized array is not a range. It is passed by value, not by reference.
> The problem there is IFTI thinking you want to pass the fixed array as a fixed
> array and not as a slice.
> 2. a container is not a range. An Array is a container, so you must extract a
> range from it to use it in range-like activities.
>
> The second point seems odd, since builtin arrays are ranges, but an Array is
> different because it's a true reference type (changing the length from one
> reference alters the length of another reference) and it "owns" the memory
> contained within, unlike a builtin array which just references the memory.
>
> But it's also easy to consider other things. Consider a RedBlackTree container,
> should that be a range? What happens when you popFront?

Isn't there a step to pass toward integration of builtin collections and 
ranges. Should be transparent from the language-side. There are still, I guess, 
far too many implementation details leaking into language semantics. Python is 
a model for that.

Denis
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