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Re: operator overloading
by Warner Onstine-3
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On 10/1/07, Tom Nichols <tmnichols@...> wrote:
> Here's a quick test... let me know if there's something I missed that
> doesn't fit your requirements:
>
> class MySet implements Comparable {
> def items = []
> public int compareTo(Object other) {
> if( ! (other instanceof MySet) ) return -1
>
> def diff = (this.items - other.items).size
> if( diff != 0 ) return diff
> (other.items - this.items).size *-1
> }
> }
>
> def set1 = new MySet( items:[1,2,3] )
> def set2 = new MySet( items:[1,2,3] )
> assert set1 == set2
>
> set2.items -= 3
> assert set1 != set2
> assert set2 <= set1
> assert set1 > set2
Honestly, I'm not even sure what this is testing, sorry.
>
> set3 = new MySet( items:[1,8] )
> assert set3 != set1
> assert set3 >= set1
This last one is false it should be assert !(set3 >= set1) as not all
elements of set1 are in set3 (which is a requirement of being a
superset, or subset - whichever way you look at it).
Just for edification:
a <= b means that all elements in a are also in b (and they could be
equal as is the same as b)
a < b means that all elements in a are also in b (and they can't be equal)
Without knowing which method call is happening I can't logically tell
what I should be returning. If I had direct access to
compareLessThanEqualsTo then I could say it is either true or false
based on what I know at the time, but this way I have to guess in what
context I'm calling compareTo.
Bottom line is after looking at this some more I think it just isn't
doable in Groovy right now.
-warner
>
> On 10/1/07, Warner Onstine <warnero@...> wrote:
> > On 10/1/07, Barzilai Spinak <barcho@...> wrote:
> > > Some points to consider:
> > > 1) In order to use the <, <=, >, >= operators, the operands (or at least
> > > the left operand) must implement Comparable
> >
> > Which seems an unfortunate choice from my perspective.
> >
> > > 2) If the implement Comparable, they must have the method: public int
> > > compareTo(Object other)
> > > 3) This method returns an int, which normally has the semantics that:
> > > * it must be less than zero if this object is less than "other"
> > > * it must be greater than zero if this object is greater than "other"
> > > * it must be zero if this object is equal to "other" (which, for
> > > consistency reaons, should behave like the equals method in this case)
> > > 4) Normally in Groovy the == and != operator will call the equals method
> > > of the left operand, passing the right operand.
> > > * BUT* if the objects implement Comparable (as yours will do), then
> > > it calls the compareTo method as explained
> >
> > That seems like an even worse problem (especially in my situation right now)
> >
> > > 5) Even though compareTo returns an integer, the comparator operators
> > > return a boolean (you normally won't call compareTo directly).
> >
> > Finally found that chart in GinA. But I don't know if it's going to
> > help me with what I *need* to do.
> >
> > > 6) There are (or used to be) some weird cases for equals that have been
> > > discussed in the list in the past but I don't remember the details now :-)
> > >
> > > One last question, when you say (a <= b), do you want to DECLARE a
> > > relation or TEST for its truth?
> >
> > Test for its truth. if a is a subset of b (ie - all of a's elements
> > are in b, and/or a equals b). This leads me right into my main issue
> > here. If I do a comparison of two sets a and b.
> > a = [1,2,3] (assume this is my custom class)
> > b = [1,2,3,4,5,6]
> >
> > and I do
> > a <= b this should return true, but if I now have
> > c = [1,8]
> > c <= b this should be false (because not all elements of c are in b)
> > but I don't know what I should be returning from compareTo in this
> > instance, it isn't less, it isn't equals, it isn't greater than, it's
> > just false. So, it is beginning to look more and more like I can't do
> > what I want to do with operator overloading here.
> >
> > Someone please correct me if I'm wrong.
> >
> > -warner
> >
> > >
> > > I hope this helps.
> > >
> > > BarZ
> > >
> > >
> > > Warner Onstine wrote:
> > > > Ok, I'm having some amount of difficulty with trying implement some
> > > > operator overloading and am hoping someone has some ideas on how to
> > > > fix these issues.
> > > >
> > > > Here's what I'm trying to do (and didn't think it would be this
> > > > difficult). I want to implement some Set notation like the following:
> > > > a is a subset of b (a <= b)
> > > > a is a proper subset of b (a < b)
> > > > a equals b (a == b)
> > > >
> > > > and some Set operations:
> > > > a union b (a + b)
> > > > a intersect b (a / b)
> > > > a complement b (a - b)
> > > >
> > > > For reference set notation and operations can be found on wikipedia
> > > > (http://en.wikipedia.org/wiki/Naive_set_theory).
> > > >
> > > > Now that I have the ground rules laid here are some of the issues I'm
> > > > encountering:
> > > > 1) a == b, do this by overriding the equals method, right? Nope, the
> > > > compareTo(object) method gets called instead
> > > > 2) a <= b, i have to implement Comparable to use the compareTo()
> > > > method (which by the way is not at all mentioned here -
> > > > http://groovy.codehaus.org/Operator+Overloading). But the compareTo()
> > > > method only returns -1, 0, or 1 (not true or false, which is needed
> > > > for my tests and would make sense to me)
> > > >
> > > > Please tell me I'm wrong, I would love to be wrong on this. But this
> > > > seems overly complicated for overriding some of these methods. I know
> > > > that the leftShift operator is not nearly as difficult (and seems to
> > > > be the one that everyone goes after).
> > > >
> > > > I'm attaching my test class and actual class I'm using. I also tried
> > > > initially to use ExpandoMetaClass to do this but kept getting argument
> > > > type mismatches when I called. This led me down my current path of
> > > > using my own class as originally I wanted to use this on all
> > > > Collections.
> > > >
> > > >
> > > > ------------------------------------------------------------------------
> > > >
> > > > ---------------------------------------------------------------------
> > > > To unsubscribe from this list please visit:
> > > >
> > > > http://xircles.codehaus.org/manage_email
> > >
> > >
> > > ---------------------------------------------------------------------
> > > To unsubscribe from this list please visit:
> > >
> > > http://xircles.codehaus.org/manage_email
> > >
> > >
> >
> >
> > --
> > Warner Onstine - Programmer/Author
> > New book on Tapestry 4!
> > Tapestry 101 available at
> > http://sourcebeat.com/books/tapestrylive.html
> > warner@...
> > http://warneronstine.com/blog
> >
> > ---------------------------------------------------------------------
> > To unsubscribe from this list please visit:
> >
> > http://xircles.codehaus.org/manage_email
> >
> >
>
> ---------------------------------------------------------------------
> To unsubscribe from this list please visit:
>
> http://xircles.codehaus.org/manage_email
>
>
--
Warner Onstine - Programmer/Author
New book on Tapestry 4!
Tapestry 101 available at
http://sourcebeat.com/books/tapestrylive.html
warner@...
http://warneronstine.com/blog
---------------------------------------------------------------------
To unsubscribe from this list please visit:
http://xircles.codehaus.org/manage_email
> Here's a quick test... let me know if there's something I missed that
> doesn't fit your requirements:
>
> class MySet implements Comparable {
> def items = []
> public int compareTo(Object other) {
> if( ! (other instanceof MySet) ) return -1
>
> def diff = (this.items - other.items).size
> if( diff != 0 ) return diff
> (other.items - this.items).size *-1
> }
> }
>
> def set1 = new MySet( items:[1,2,3] )
> def set2 = new MySet( items:[1,2,3] )
> assert set1 == set2
>
> set2.items -= 3
> assert set1 != set2
> assert set2 <= set1
> assert set1 > set2
Honestly, I'm not even sure what this is testing, sorry.
>
> set3 = new MySet( items:[1,8] )
> assert set3 != set1
> assert set3 >= set1
This last one is false it should be assert !(set3 >= set1) as not all
elements of set1 are in set3 (which is a requirement of being a
superset, or subset - whichever way you look at it).
Just for edification:
a <= b means that all elements in a are also in b (and they could be
equal as is the same as b)
a < b means that all elements in a are also in b (and they can't be equal)
Without knowing which method call is happening I can't logically tell
what I should be returning. If I had direct access to
compareLessThanEqualsTo then I could say it is either true or false
based on what I know at the time, but this way I have to guess in what
context I'm calling compareTo.
Bottom line is after looking at this some more I think it just isn't
doable in Groovy right now.
-warner
>
> On 10/1/07, Warner Onstine <warnero@...> wrote:
> > On 10/1/07, Barzilai Spinak <barcho@...> wrote:
> > > Some points to consider:
> > > 1) In order to use the <, <=, >, >= operators, the operands (or at least
> > > the left operand) must implement Comparable
> >
> > Which seems an unfortunate choice from my perspective.
> >
> > > 2) If the implement Comparable, they must have the method: public int
> > > compareTo(Object other)
> > > 3) This method returns an int, which normally has the semantics that:
> > > * it must be less than zero if this object is less than "other"
> > > * it must be greater than zero if this object is greater than "other"
> > > * it must be zero if this object is equal to "other" (which, for
> > > consistency reaons, should behave like the equals method in this case)
> > > 4) Normally in Groovy the == and != operator will call the equals method
> > > of the left operand, passing the right operand.
> > > * BUT* if the objects implement Comparable (as yours will do), then
> > > it calls the compareTo method as explained
> >
> > That seems like an even worse problem (especially in my situation right now)
> >
> > > 5) Even though compareTo returns an integer, the comparator operators
> > > return a boolean (you normally won't call compareTo directly).
> >
> > Finally found that chart in GinA. But I don't know if it's going to
> > help me with what I *need* to do.
> >
> > > 6) There are (or used to be) some weird cases for equals that have been
> > > discussed in the list in the past but I don't remember the details now :-)
> > >
> > > One last question, when you say (a <= b), do you want to DECLARE a
> > > relation or TEST for its truth?
> >
> > Test for its truth. if a is a subset of b (ie - all of a's elements
> > are in b, and/or a equals b). This leads me right into my main issue
> > here. If I do a comparison of two sets a and b.
> > a = [1,2,3] (assume this is my custom class)
> > b = [1,2,3,4,5,6]
> >
> > and I do
> > a <= b this should return true, but if I now have
> > c = [1,8]
> > c <= b this should be false (because not all elements of c are in b)
> > but I don't know what I should be returning from compareTo in this
> > instance, it isn't less, it isn't equals, it isn't greater than, it's
> > just false. So, it is beginning to look more and more like I can't do
> > what I want to do with operator overloading here.
> >
> > Someone please correct me if I'm wrong.
> >
> > -warner
> >
> > >
> > > I hope this helps.
> > >
> > > BarZ
> > >
> > >
> > > Warner Onstine wrote:
> > > > Ok, I'm having some amount of difficulty with trying implement some
> > > > operator overloading and am hoping someone has some ideas on how to
> > > > fix these issues.
> > > >
> > > > Here's what I'm trying to do (and didn't think it would be this
> > > > difficult). I want to implement some Set notation like the following:
> > > > a is a subset of b (a <= b)
> > > > a is a proper subset of b (a < b)
> > > > a equals b (a == b)
> > > >
> > > > and some Set operations:
> > > > a union b (a + b)
> > > > a intersect b (a / b)
> > > > a complement b (a - b)
> > > >
> > > > For reference set notation and operations can be found on wikipedia
> > > > (http://en.wikipedia.org/wiki/Naive_set_theory).
> > > >
> > > > Now that I have the ground rules laid here are some of the issues I'm
> > > > encountering:
> > > > 1) a == b, do this by overriding the equals method, right? Nope, the
> > > > compareTo(object) method gets called instead
> > > > 2) a <= b, i have to implement Comparable to use the compareTo()
> > > > method (which by the way is not at all mentioned here -
> > > > http://groovy.codehaus.org/Operator+Overloading). But the compareTo()
> > > > method only returns -1, 0, or 1 (not true or false, which is needed
> > > > for my tests and would make sense to me)
> > > >
> > > > Please tell me I'm wrong, I would love to be wrong on this. But this
> > > > seems overly complicated for overriding some of these methods. I know
> > > > that the leftShift operator is not nearly as difficult (and seems to
> > > > be the one that everyone goes after).
> > > >
> > > > I'm attaching my test class and actual class I'm using. I also tried
> > > > initially to use ExpandoMetaClass to do this but kept getting argument
> > > > type mismatches when I called. This led me down my current path of
> > > > using my own class as originally I wanted to use this on all
> > > > Collections.
> > > >
> > > >
> > > > ------------------------------------------------------------------------
> > > >
> > > > ---------------------------------------------------------------------
> > > > To unsubscribe from this list please visit:
> > > >
> > > > http://xircles.codehaus.org/manage_email
> > >
> > >
> > > ---------------------------------------------------------------------
> > > To unsubscribe from this list please visit:
> > >
> > > http://xircles.codehaus.org/manage_email
> > >
> > >
> >
> >
> > --
> > Warner Onstine - Programmer/Author
> > New book on Tapestry 4!
> > Tapestry 101 available at
> > http://sourcebeat.com/books/tapestrylive.html
> > warner@...
> > http://warneronstine.com/blog
> >
> > ---------------------------------------------------------------------
> > To unsubscribe from this list please visit:
> >
> > http://xircles.codehaus.org/manage_email
> >
> >
>
> ---------------------------------------------------------------------
> To unsubscribe from this list please visit:
>
> http://xircles.codehaus.org/manage_email
>
>
--
Warner Onstine - Programmer/Author
New book on Tapestry 4!
Tapestry 101 available at
http://sourcebeat.com/books/tapestrylive.html
warner@...
http://warneronstine.com/blog
---------------------------------------------------------------------
To unsubscribe from this list please visit:
http://xircles.codehaus.org/manage_email
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