[Issue 9599] File.byLine doesn't function properly with take

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=9599


monarchdodra at gmail.com changed:

           What    |Removed                     |Added
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                 CC|                            |monarchdodra at gmail.com


--- Comment #1 from monarchdodra at gmail.com 2013-02-27 03:35:11 PST ---
(In reply to comment #0)
> Using 2.062, Regarding the following code:

The bug is actually inside byLine itself, so we can remove take from the
equation. The problem is that byLine is over-eager:
1) Creating a front element eagerly pops that element.
2) poping an element eagerlly parses the next, effectivelly popping it off too
if it is never read:

Reduced test showing this:

//----
import std.stdio;

void main()
{
   auto file = File.tmpfile();
   file.write("1\n2\n3\n4\n5");
   file.rewind();

   auto fbl1 = file.byLine();
   writeln(fbl1.front); //prints 1.

   auto fbl2 = file.byLine();
   writeln(fbl2.front); //prints 2... Wait. Who popped off 1?
   fbl2.popFront();     //pops off 2, and consumes 3.

   auto fbl3 = file.byLine();
   writeln(fbl3.front); //prints 4.
}
//----

Ideally, byLine should be reworked to be a little more lazy, and better
preserve the integrity of its underlying stream:
- "front means do NOT modify the referenced container"
- "pop means remove the CURRENT element, and stop there"

byLine is obviously not doing that. The fact that it is *just* an input range
does not mean it gets to bypass standard rules.

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