dmd/compiler/test/fail_compilation/test8556.d

/*
TEST_OUTPUT:
---
fail_compilation/test8556.d(24): Error: template instance `test8556.Grab!(Circle!(uint[]))` does not match template declaration `Grab(Range)`
  with `Range = Circle!(uint[])`
  must satisfy the following constraint:
`       !isSliceable!Range`
fail_compilation/test8556.d(55): Error: template instance `test8556.grab!(Circle!(uint[]))` error instantiating
---
*/

extern(C) int printf(const char*, ...);

template isSliceable(R)
{
    enum bool isSliceable = is(typeof( R.init[1 .. 2] ));
}

struct Grab(Range) if (!isSliceable!Range)
{
    public Range source;
}

Grab!R grab(R)(R input)
{
    return Grab!R(input);
}

// 3. evaluate isSliceable in template constraint
auto grabExactly(R)(R range) if (!isSliceable!R) { return 0; }
auto grabExactly(R)(R range) if ( isSliceable!R) { return 0; }

struct Circle(Range)
{
    // 2. auto return opSlice
    auto opSlice(size_t i, size_t j)
    {
        //pragma(msg, typeof(opSlice)); // prints "fwdref err" with B, but doesn't with A

        printf("%d %d\n", cast(int)i, cast(int)j);
        assert(j >= i);

        // 1. grabExactly curcular refers this opSlice.
        return grabExactly(typeof(this)());     // broken execution with A
    }
}

Circle!R circle(R)()
{
    return Circle!R();
}

void main()
{
    auto t = grab(circle!(uint[])());

    auto cx = circle!(uint[])();
    auto slice = cx[23 .. 33];
}