wrong isInputRange design

[rumbu via Digitalmars-d]

On Saturday, 3 December 2016 at 16:37:21 UTC, Jerry wrote:
> On Saturday, 3 December 2016 at 11:52:00 UTC, rumbu wrote:
>> import std.range.primitives: isInputRange;
>>
>> void test(R)(ref R range) if (isInputRange!R)
>> {
>>     auto c = r.front; //Error: no property 'front' for type 
>> 'string'	
>> }
>>
[...]
>>
>> import std.range.primitives: isInputRange, ElementType;
>> import std.traits: isSomeChar;
>>
>> void foo(C)(const(C)[] array) if (isSomeChar!C)
>> {
>>     //this will be never called	
>> }
>>
>> void foo(R)(ref R range) if (isInputRange!R && 
>> isSomeChar!(ElementType!R))
>> {
>>     //this will be always called
>>     //any call to range.front, range.empty and so on will 
>> result in error
>> }
>>
>> foo(somestring)
>>
>> I expect foo!string to be called instead of foo!Range, because 
>> in my context isInputRange!string should return false. 
>> Instead, my context is hijacked by the definitions spread 
>> along std.range.primitives module.
>>
>> The workaround I found is to define the second overload like 
>> this:
>>
>> void foo(R)(ref R range) if (isInputRange!R && !isSomeString!R 
>> && isSomeChar!(ElementType!R))
>
> Is that the exact code? isInputRange checks to see if the type 
> has "front" defined.

>
> https://github.com/dlang/phobos/blob/v2.072.0/std/range/primitives.d#L162
>
> Also "string" is just an alias of an array, 
> "immutable(char)[]". So an array should have "front" defined. 
> Can you post more code?

No, an array should not have "front" defined according to D 
language specification. "front" for arrays is defined in 
std.range.primitives. That's the problem, I cannot have two 
specialized functions (one taking arrays and one taking ranges), 
because std.range.primitives hijacks any char array and 
transforms it in a range). front, empty, popFront must not be 
defined for arrays in the same module as isInputRange.

Exact code is irrelevant, but you're welcome:

string constructor: 
https://github.com/rumbu13/numerics/blob/master/src/numerics/fixed.d#L978

range constructor
https://github.com/rumbu13/numerics/blob/master/src/numerics/fixed.d#L1104