On Tuesday, 17 February 2015 at 13:38:41 UTC, Per Nordlöw wrote:
This looses most of the meaning of my idea. I still want my
range to inherit all the powers of its wrapped range.
Is there no way to disable member functions in D?
I hadn't thought of @disable. Played around with it a bit. The
following code seems to work. I didn't really test it or think
very hard about it, though.
Regarding opIndexAssign: Without it, alias this jumps in on
assignments, and the ref opIndex is not considered. This may be a
compiler bug.
Be aware that with alias this, IndexedBy!(R, I) implicitly
converts to R. So it's easy to (accidentally) fall back to a
plain R, where nothing is `@disable`d. I don't know if this is
desirable or not.
----
struct Ix(T = size_t)
{
@safe pure: @nogc nothrow:
this(T ix) { this._ix = ix; }
alias _ix this;
private T _ix = 0;
}
struct IndexedBy(R, I)
{
auto ref opIndex(I ix) inout { return _r[ix]; }
void opIndexAssign(V)(V value, I ix) {_r[ix] = value;}
alias RI = size_t; /* TODO: Extract this from R somehow. */
static if(!is(RI == I))
{
@disable void opIndex(RI i);
@disable void opIndexAssign(V)(V value, RI i);
}
R _r;
alias _r this;
}
auto indexedBy(I, R)(R range)
{
return IndexedBy!(R, I)(range);
}
unittest
{
import std.stdio;
auto x = [1, 2, 3];
alias I = int;
auto ix = x.indexedBy!I;
ix[0] = 11;
alias J = Ix!size_t;
auto jx = x.indexedBy!J;
jx[J(0)] = 11;
static assert(!__traits(compiles, (jx[0] = 11)));
}
----
