On Sun, 24 Jul 2011 10:51:32 -0400, Lutger Blijdestijn
<[email protected]> wrote:
Jonathan M Davis wrote:
On Sunday 24 July 2011 12:06:47 Lutger Blijdestijn wrote:
I'm trying to have a Cycle range of a static array as a struct member,
but getting a compilation error. Can anybody tell me if I'm doing
something wrong, or is this a bug?
import std.range;
struct Foo
{
ubyte[] buf;
Cycle!(typeof(buf)) cbuf1; // ok
ubyte[1024] staticBuf;
Cycle!(typeof(staticBuf)) cbuf2; // error
void test()
{
Cycle!(typeof(staticBuf)) cbuf3;
cbuf3 = cycle(staticBuf); // ok
}
}
/std/range.d(228): Error: template instance
std.array.front!(ubyte[1024u]) incompatible arguments for template
instantiation
static arrays are not ranges. You can't pop the front off of them, so no
range- based algorithm would work with a static range. Now, you _can_
get
a dynamic range over a static range and _that_ is a valid range, so what
you need to do is make the Cycle a Cycle!(ubyte[]) rather than
Cycle!(ubyte[1024]), and you when you pass the static array to cycle,
you
need to slice it: cycle(staticBuf[]).
- Jonathan M Davis
That would work, but the docs explicitly mention that Cycle is
specialized
for static arrays (for performance reasons). This is how cycle is
implemented:
Cycle!(R) cycle(R)(ref R input, size_t index = 0) if (isStaticArray!R)
{
return Cycle!(R)(input, index);
}
This is definitely a bug. In fact, it's a regression, since it passes on
2.051 (fails on 2.052 and later). The error is occurring during the
execution of the *template constraint*.
Reduced case:
import std.range;
pragma(msg, isInputRange!(ubyte[2u]).stringof);
If it's not a bug in dmd (or rather it's the result of a fixed bug), then
it's a bug in Phobos' isInputRange implementation. However, I doubt
that. Also, the same line works in the context of a function:
import std.range;
void main()
{
pragma(msg, isInputRange!(ubyte[2u]).stringof); // no error
}
Please file a 'rejects-valid' bug.
-Steve
