On Friday, 17 July 2015 at 07:42:09 UTC, Roland Hadinger wrote:
Here's how I would implement the basic behaviour (could be
extended to also forward bidirectional and random access
functions):
---
auto cushion(R)(R r)
if (isInputRange!R)
{
static if (isInfinite!R) { return r; } else {
struct _Cushion(R)
{
R r;
alias E = ElementType!R;
alias NE = Nullable!E;
@property bool empty() { return false; }
@property NE front()
{
return !r.empty ? NE(r.front) : NE();
}
void popFront()
{
if (!r.empty) r.popFront();
}
}
return _Cushion!R(r);
}
}
---
I didn't find anything like this Phobos. Did I miss something?
The building blocks are there. You're `map`ping the original
range to `Nullable`, and then you're `chain`ing an infinite range
(`cycle`) of nulls behind.
----
import std.range: isInputRange;
auto cushion(R)(R r)
if (isInputRange!R)
{
import std.algorithm: map;
import std.range: chain, cycle, ElementType, only;
import std.typecons: Nullable;
alias E = ElementType!R;
alias NE = Nullable!E;
return chain(r.map!NE, NE().only.cycle);
}
----
