Add .save property to PermutedCongruentialEngine when stream type is …

…stream_t.specific (#131)

source/mir/random/engine/pcg.d

@@ -226,12 +226,13 @@ public:
         /++
         Compatibility with $(LINK2 https://dlang.org/phobos/std_random.html#.isUniformRNG,
         Phobos library methods). Presents this RNG as an InputRange.
-        Only available if `output_previous == true`. `save` is available when
-        `streamType` is `stream_t.none` or `stream_t.oneseq`.
+        Only available if `output_previous == true`.
 
         The reason that this is enabled when `output_previous == true` is because
         `front` can be implemented without additional cost.
 
+        `save` is implemented if `streamType` is not [stream_t.unique].
+
         This struct disables its default copy constructor and so will only work with
         Phobos functions that "do the right thing" and take RNGs by reference and
         do not accidentally make implicit copies.
@@ -248,7 +249,7 @@ public:
         /// ditto
         void seed()(Uint seed) { this.__ctor(seed); }
         /// ditto
-        static if (streamType == stream_t.none || streamType == stream_t.oneseq)
+        static if (streamType != stream_t.unique)
         @property typeof(this) save()() const
         {
             typeof(return) result = void;
@@ -272,24 +273,18 @@ public:
     {
         static assert(isPhobosUniformRNG!(RNG, typeof(RNG.max)));
         static assert(isSeedable!(RNG, RNG.Uint));
+        static assert(isForwardRange!RNG);
         auto gen1 = RNG(1);
         auto gen2 = RNG(2);
-        static if (__traits(hasMember, RNG, "save"))
-        {
-            static assert(isForwardRange!RNG);
-            auto gen3 = gen1.save;
-        }
+        auto gen3 = gen1.save;
         gen2.seed(1);
         assert(gen1 == gen2);
         immutable a = gen1.front;
         gen1.popFront();
         assert(a == gen2());
         assert(gen1.front == gen2());
-        static if (is(typeof(gen3)))
-        {
-            assert(a == gen3());
-            assert(gen1.front == gen3());
-        }
+        assert(a == gen3());
+        assert(gen1.front == gen3());
     }
 
     foreach(RNG; AliasSeq!(pcg32_unique))
@@ -434,9 +429,7 @@ mixin template specific_stream(Uint)
     ///
     Uint inc_ = default_increment!Uint;
     ///
-    @property Uint increment()() { return inc_; }
-    ///
-    @property void increment()(Uint u) { inc_ = u;}
+    alias increment = inc_;
     ///
     enum can_specify_stream = true;
     ///