# Preserve value-type semantics in imported types **URL:** \ **Category:** Ruby\ **Created:** [February 10, 2006, 9:00pm UTC](https://www.ruby-forum.com/t/preserve-value-type-semantics-in-imported-types/65523 "2006-02-10T21:00:48Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![johnlester](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e480ec/32.png) [@johnlester](https://www.ruby-forum.com/u/johnlester)\ **Post date:** [February 10, 2006, 9:00pm UTC](https://www.ruby-forum.com/t/preserve-value-type-semantics-in-imported-types/65523/1 "2006-02-10T21:00:48Z")
I’m importing a value type from the CLR and I’d like to preserve value type semantics in Ruby … I’m not sure this can be done. Consider the Point struct in C# as an example: Point p1 = new Point(2, 3); Point p2 = p1; // value types get copied in the CLR upon assignment p2.X += 1; Assert.Equals(p1.X + 1, p2.X); So the equivalent code that uses my RubyCLR bridge doesn’t display the equivalent semantics: p1 = Point.new(2, 3) p2 = p1 # the object reference gets copied in Ruby, so this is now an alias p2.X += 1 assert\_equal p1.X, p2.X The value types are stored as opaque blobs in Ruby’s T\_DATA struct. Since I can’t overload the assignment operator, are there any tricks that can help me? Or do I have to write a custom implementation of clone for value types that memcpys the T\_DATA struct? Thanks -John > **[John Lam's Blog](https://www.iunknown.com/)** > > Since 1997 ---
**Author:** ![johnlester](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e480ec/32.png) [@johnlester](https://www.ruby-forum.com/u/johnlester)\ **Post date:** [February 10, 2006, 11:03pm UTC](https://www.ruby-forum.com/t/preserve-value-type-semantics-in-imported-types/65523/2 "2006-02-10T23:03:39Z")
Dear John, Welcome to ref-value world! I am not sure what is your problem in real, but I might suggest you to read the clone and dup methods of Object class at [http://www.ruby-doc.org/core](http://www.ruby-doc.org/core) Don’t you think how deep your need to copy an object is case by case after all? I leave here three samples below. sorry, if I haven’t got the point. BTW you wrote p1.X, p1.Y and so on, but starting with a capital letter means a constant in Ruby language. If you were about to mean variables, they should start with a small such that p1.x, p1.y… cheers, nori ---
**Author:** ![johnlester](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e480ec/32.png) [@johnlester](https://www.ruby-forum.com/u/johnlester)\ **Post date:** [February 10, 2006, 11:21pm UTC](https://www.ruby-forum.com/t/preserve-value-type-semantics-in-imported-types/65523/3 "2006-02-10T23:21:07Z")
Thanks, Nori! Perhaps it wasn’t super clear in my example, but this line of code: p = Point.new(3, 4) actually creates a new CLR Point value type inside of a Ruby VALUE object. A CLR value type is an opaque blob of data (but in this case is really a couple of 32 bit integers packed together), so I store it in a T\_DATA struct. So I allocate enough memory to hold the value type, and tell the CLR to create the value type at the address of the T\_DATA struct in the VALUE object. X and Y are properties defined in the Point value type class in the CLR. They map to accessor methods get/set\_X and get/set\_Y. My RubyCLR bridge maps these things automagically through liberal use of const\_missing and method\_missing. So I can’t change these names even if they aren’t Ruby-esque. Those are the case-sensitive method and property names defined by the value type in the CLR. I guess the real issue is that I don’t think there’s a way to force value type semantics onto Ruby reference types. It would be nice to preserve CLR value type semantics inside of Ruby, but hey- they’re different type systems so you need to abide by the rules of those type systems. I’m just worried that it might introduce bugs in code that use my bridge: p1 = p2 is just so much more intuitive than p1 = p2.clone If you’re curious about my RubyCLR bridge, you can download my first public drop of the bits here: [http://www.iunknown.com/articles/2006/01/12/first-drop-of-rubyclr](http://www.iunknown.com/articles/2006/01/12/first-drop-of-rubyclr) I’m working on a new drop that marshals value types correctly - hence this question on the list. Hopefully I’ll have support early next week for folks to play with. Thanks -John > **[John Lam's Blog](https://www.iunknown.com/)** > > Since 1997 ---
**Author:** ![johnlester](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e480ec/32.png) [@johnlester](https://www.ruby-forum.com/u/johnlester)\ **Post date:** [February 11, 2006, 2:15am UTC](https://www.ruby-forum.com/t/preserve-value-type-semantics-in-imported-types/65523/4 "2006-02-11T02:15:34Z")
sorry John, I forgot to paste the sample code, but it may not be necessary as you already know clone and dup. I have just browsed RubyCLR and some more. However, let me excuse writing here rather general things because I haven’t read your program carefully. As you already know, we cannot assume classes of arguments when we make libraries in ruby, and types we use in ruby are not fully the same as those in the system. But I am not worried, wish neither would you be. It seems that the types you need to keep right are not of values inside ruby programs, but of those to interface to outside ruby, that is the places we carefully use ruby-\>C and C-\>ruby functions, right? Such type information in ruby objects shall be only accessible to read so that ruby applications do not change. I guess everybody overcome p2 = p1 and p2 = pl.clone strangeness sooner or later 🙂 greetings to you, Mathew, Ben and their mom… and more? nori ---
**Author:** ![johnlester](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e480ec/32.png) [@johnlester](https://www.ruby-forum.com/u/johnlester)\ **Post date:** [February 11, 2006, 12:02am UTC](https://www.ruby-forum.com/t/preserve-value-type-semantics-in-imported-types/65523/5 "2006-02-11T00:02:08Z")
On Feb 10, 2006, at 5:20 PM, John L. wrote: > I’m just worried that it might introduce bugs in code that use my > bridge: > > p1 = p2 is just so much more intuitive than p1 = p2.clone In the eye of the beholder… I like that Ruby insists on uniform semantics for assignment. As such, I don’t ever have to consider if p1 = p2 is really p1 = p2.clone Side note: Is it fair to say that Object#clone should be written such that b = a.clone always results in (a == b) being true and (a.equal?(b)) being false? Is it OK for clone to return self or should an exception be raised as with Fixnum, Symbol, etc. when a new instance would break the value/identity semantics of the class? Gary W.