improve error message

Author: 9il

source/mir/ndslice/internal.d

@@ -153,10 +153,8 @@ size_t[] reverse()(size_t[] ar)
     return ar;
 }
 
-enum indexError(size_t pos, size_t N) =
-    "index at position " ~ pos.stringof
-    ~ " from the range [0 .." ~ N.stringof ~ ")"
-    ~ " must be less than corresponding length.";
+enum indexError(DeepElement, int pos, int N) =
+    N.stringof ~ "D slice of " ~ DeepElement.stringof ~ ": bounds check failed at " ~ (pos + 1).stringof ~ " dimension";
 
 enum string tailErrorMessage(
     string fun = __FUNCTION__,

source/mir/ndslice/slice.d

@@ -785,39 +785,39 @@ package(mir):
             static if (kind == Contiguous)
             {
                 enum E = I - 1;
-                assert(_indices[E] < _lengths[E], indexError!(E, N));
+                assert(_indices[E] < _lengths[E], indexError!(DeepElement, E, N));
                 ptrdiff_t ball = this._stride!E;
                 ptrdiff_t stride = _indices[E] * ball;
                 foreach_reverse (i; Iota!E) //static
                 {
                     ball *= _lengths[i + 1];
-                    assert(_indices[i] < _lengths[i], indexError!(i, N));
+                    assert(_indices[i] < _lengths[i], indexError!(DeepElement, i, N));
                     stride += ball * _indices[i];
                 }
             }
             else
             static if (kind == Canonical)
             {
                 enum E = I - 1;
-                assert(_indices[E] < _lengths[E], indexError!(E, N));
+                assert(_indices[E] < _lengths[E], indexError!(DeepElement, E, N));
                 static if (I == N)
                     size_t stride = _indices[E];
                 else
                     size_t stride = _strides[E] * _indices[E];
                 foreach_reverse (i; Iota!E) //static
                 {
-                    assert(_indices[i] < _lengths[i], indexError!(i, N));
+                    assert(_indices[i] < _lengths[i], indexError!(DeepElement, i, N));
                     stride += _strides[i] * _indices[i];
                 }
             }
             else
             {
                 enum E = I - 1;
-                assert(_indices[E] < _lengths[E], indexError!(E, N));
+                assert(_indices[E] < _lengths[E], indexError!(DeepElement, E, N));
                 size_t stride = _strides[E] * _indices[E];
                 foreach_reverse (i; Iota!E) //static
                 {
-                    assert(_indices[i] < _lengths[i], indexError!(i, N));
+                    assert(_indices[i] < _lengths[i], indexError!(DeepElement, i, N));
                     stride += _strides[i] * _indices[i];
                 }
             }