« Return to Thread: operator overloading
Re: operator overloading
by Tom Nichols
::
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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
set3 = new MySet( items:[1,8] )
assert set3 != set1
assert set3 >= set1
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
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
set3 = new MySet( items:[1,8] )
assert set3 != set1
assert set3 >= set1
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
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