includes/std: Added nullable pointers to std/ptr (#97)

includes/std/ptr.pat

@@ -34,4 +34,34 @@ namespace std::ptr {
         return std::mem::size() - offset * 2;
     };
 
+    /**
+    A nullable pointer, generic over both the pointee type and pointer type.
+
+    By nullable, we mean that if the pointer's value is zero (`0x0`), then the
+    value will appear as padding rather than a pointer to something, but
+    if the pointer's value is non-zero, that non-zero value will be treated as
+    a pointer of type `PointerTy` which points to an element of type `PointeeTy`.
+
+    Example:
+    A struct field called `p_myInfo` which is a nullable 64-bit pointer to an
+    element of type `MyInfoTy` would be written as:
+    ```
+    struct MyStruct {
+      std::ptr::NullablePtr<MyInfoTy, u64> p_myInfo;
+    }
+    ```
+    */
+    struct NullablePtr<PointeeTy, PointerTy> {
+        // `pointerValue` is `no_unique_address` because we don't want to advance
+        // the current memory location after reading the value of the pointer itself;
+        // we want to examine the value at this address to determine what should be
+        // displayed. It's also `hidden` so the editor only displays either thee 
+        // padding or the populated pointer/pointee field.
+        PointerTy pointerValue [[no_unique_address, hidden]];
+        if (pointerValue == 0x0) {
+            padding[sizeof(PointerTy)];
+        } else {
+            PointeeTy *data : PointerTy;
+        }
+    };
 }