Understanding isInfinite(Range)

[Stanislav Blinov]

Andrej Mitrovic wrote:
> I'd love to see this used more in Phobos. I don't know if there are any drawbacks, but this looks and works nicely:
> 
> import std.stdio : writeln;
> 
> void main()
> {
>     writeln(isInputRange!(N));
> }
> 
> class N
> {
>     N test;
>     
>     bool empty()
>     {
>         return false;
>     }
>     
>     @property
>     void popFront()
>     {
>     }
>     
>     @property
>     N front()
>     {
>         return test;
>     }
> }
> 
> 
> template isInputRange(R)
> {
>     enum bool isInputRange = __traits(compiles,
>     {
>         R r;             // can define a range object
>         if (r.empty) {}  // can test for empty
>         r.popFront;          // can invoke next
>         auto h = r.front; // can get the front of the range
>     });
> }
> 
> If you uncomment some of those methods in class N, then you get back false, which is what you want. Currently isInputRange is defined like so in Phobos:
> 
> template isInputRange(R)
> {
>     enum bool isInputRange = is(typeof(
>     {
>         R r;             // can define a range object
>         if (r.empty) {}  // can test for empty
>         r.popFront;          // can invoke next
>         auto h = r.front; // can get the front of the range
>     }()));
> }
> 
> It's getting close to LISP! :)
> 

If I remember correctly, it has been discussed not long ago that those 
is(typeof(...))s should really be __traits(compiles). Maybe it's just 
some code was written before those lovely __traits were introduced?..