Type-Strict Indexes: IndexedBy

["Nordlöw" via Digitalmars-d-learn]

I'm trying to figure out how to implement a light-weight wrappr 
realizing type-safe indexing á lá Ada. Here's my first try:

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]; }
     auto ref opSlice(I lower, I upper) inout { return _r[lower .. 
upper]; }
     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;              // should compile
     jx[0] = 11;                 // TODO how can I make this not 
compile?
}

My question now of course is:

How can I prevent

     jx[0] = 11;

from compiling?