How to work with an "arbitrary input range"?

[Adam D. Ruppe]

I've seen the requirement tossed around a few times that functions should work
with arbitrary input ranges.

What, exactly, does this mean?

My first impression is:

void myFunction(T)(T t) if(isInputRange!(T)) {}

But I don't see how that actually works in practice. Suppose my function
parses some kind of text format, like D code or XML. It won't work with a
stream of integers.

OK, what about:

void myFunction(T)(T t) if(isSomeString!(T)) {}


The function could certainly work with that, but it doesn't seem to me to be
an arbitrary input range anymore; it is little different than if I just said
myFunction(string t).


Should it be something like this?

if(is(T.front : dchar))

(I'm sure that's actually wrong syntax, but hopefully you know what I mean)


That seems weak, since it wouldn't work with stdin.byLine, but perhaps it
shouldn't - the file format is char based, not line based. (should there be an
adapter range available there, to feed me one char at a time from a series of
lines? That seems to be adding a layer just to cancel out the one beneath it
though.)


Anyway, what's the right thing to do here?