Adapt code to support -preview=in

When the switch is provided, '[auto] ref in' becomes illegal in the parser. This little trick, using static if + mixin, allow to have a different function based on whether the switch is used or not.

Author: Geod24

source/mir/ndslice/internal.d

@@ -259,10 +259,24 @@ template DynamicArrayDimensionsCount(T)
  enum size_t DynamicArrayDimensionsCount = 0;
 }
 
-bool isPermutation(size_t N)(auto ref in size_t[N] perm)
+// -preview=in enabled, no need for `auto ref`
+static if (!is(typeof(mixin(q{(in ref int a) => a}))))
 {
- int[N] mask;
- return isValidPartialPermutationImpl(perm, mask);
+ bool isPermutation(size_t N)(in size_t[N] perm)
+ {
+ int[N] mask;
+ return isValidPartialPermutationImpl(perm, mask);
+ }
+}
+else // -preview=in disabled
+{
+ mixin(q{
+ bool isPermutation(size_t N)(auto ref in size_t[N] perm)
+ {
+ int[N] mask;
+ return isValidPartialPermutationImpl(perm, mask);
+ }
+ });
 }
 
 version(mir_test) unittest
@@ -328,12 +342,28 @@ private enum isReference(P) =
 alias ImplicitlyUnqual(T) = Select!(isImplicitlyConvertible!(T, Unqual!T), Unqual!T, T);
 alias ImplicitlyUnqual(T : T*) = T*;
 
-size_t lengthsProduct(size_t N)(auto ref in size_t[N] lengths)
+// -preview=in is enabled
+static if (!is(typeof(mixin(q{(in ref int a) => a}))))
 {
- size_t length = lengths[0];
- foreach (i; Iota!(1, N))
+ size_t lengthsProduct(size_t N)(in size_t[N] lengths)
+ {
+ size_t length = lengths[0];
+ foreach (i; Iota!(1, N))
  length *= lengths[i];
- return length;
+ return length;
+ }
+}
+else
+{
+ mixin(q{
+ size_t lengthsProduct(size_t N)(auto ref in size_t[N] lengths)
+ {
+ size_t length = lengths[0];
+ foreach (i; Iota!(1, N))
+ length *= lengths[i];
+ return length;
+ }
+ });
 }
 
 pure nothrow version(mir_test) unittest