avoid use of D std for vector copies

source/numem/mem/vector.d

@@ -67,6 +67,11 @@ private:
         }
     }
 
+    pragma(inline, true)
+    void memcpy(T* dst, T* src, size_t length) {
+        memcpy(dst, src, T.sizeof*length);
+    }
+
 public:
 
     /// Gets the type of character stored in the string.
@@ -133,7 +138,7 @@ public:
         this(ref vector!T rhs) {
             if (rhs.memory) {
                 this.resize_(rhs.size_);
-                this.memory[0..size_] = rhs.memory[0..rhs.size_];
+                this.memcpy(this.memory, rhs.memory, rhs.size_);
             }
         }
 
@@ -143,8 +148,11 @@ public:
         @trusted
         this(ref return scope inout(vector!T) rhs) inout {
             if (rhs.memory) {
-                (cast(vector!T)this).resize_(rhs.size_);
-                (cast(vector!T)this).memory[0..size_] = (cast(vector!T)rhs).memory[0..rhs.size_];
+                auto self = (cast(vector!T)this);
+                auto other = (cast(vector!T)rhs);
+
+                self.resize_(rhs.size_);
+                other.memcpy(self.memory, other.memory, other.size_);
             }
         }
     }