| "Öö Tiib" <ootiib@hot.ee>: Dec 12 03:47AM -0800 On Thursday, 11 December 2014 18:34:13 UTC+2, JiiPee wrote: > would do the job, the only small issue is then that Point also has them > (not a major issue for me though). Is there any other way to do this so > I could use width and height? The "distance" and "size" are similar (same) in sense that they are relative (vector) values. "point" however is absolute (location) value. Therefore there are different operations that may make sense for us to do with one or other and also the results are different. For example it does make sense to add distance to point and we will get other point. It makes sense to add distance to distance and we get resulting distance. However it does not make sense to add point to point. Similarly we may multiply (or divide) distance with scalar and get scaled distance. However it does not make sense to multiply point with scalar. Therefore if you mix (or merge) "point" and "size" up then what you will get is nonsense because the meaning of those terms is lost. There are plenty of tools in standard library to avoid writing meaningless or confusing classes. For example if you want to bind two values of type 'T' together but do not want any meaning bound to that data then you can use 'std::pair<T>' or 'std::array<T,2>' or 'std::tuple<T,T>'. These all work fine and efficiently with some difference in usage syntax (so pick what fits your taste). Usage of such abstract constructs documents that developer has now taken responsibility to follow and check any "meaning" at places of usage. |
| JiiPee <no@notvalid.com>: Dec 12 12:41PM On 12/12/2014 11:47, Öö Tiib wrote: > to add point to point. Similarly we may multiply (or divide) > distance with scalar and get scaled distance. However it does > not make sense to multiply point with scalar. hmmm, the thing is that I was planning to use Point as a (mathematical-) vector. But ye, thinking the correct name should be consider here, as Point is not necessary the same as a mathematical vector. I ll have to think about this. Although I think in computer graphics its is used a lot that Point means vector as well. Or at least they are used as if they are vectors. But I ll have to think about this... Should I then create a "Vector" instead? |
| JiiPee <no@notvalid.com>: Dec 12 01:00PM On 12/12/2014 11:47, Öö Tiib wrote: > to add point to point. Similarly we may multiply (or divide) > distance with scalar and get scaled distance. However it does > not make sense to multiply point with scalar. I was just thinking it (as a mathematician), and you are actually right! Point is actually a one dimensional thing, and vector is in 2 dimension. So probably the correct representation would be: class Point { int x,y; void setPos(int newX, int newY) {x=newX, y=newY} // ... other 1 demensinal functions }; class Vector : public Point { void multiplyByScalar(int a); }; You got me thinking :). hmmm, I think I have to re-arrange my classes now. This was a good observation. Only thing is that have to think about the Size.... what is its base class... |
| JiiPee <no@notvalid.com>: Dec 12 01:17PM On 12/12/2014 11:47, Öö Tiib wrote: > Usage of such abstract constructs documents that developer has > now taken responsibility to follow and check any "meaning" at > places of usage. So at the moment am thinking of having Point as a base class and inherit Vector from it. Size maybe needs to be a totally different class, although then I must multiply some code. |
| Paavo Helde <myfirstname@osa.pri.ee>: Dec 12 10:53AM -0600 > }; > class Vector : public Point > { As you just said, Vector is not a Point. Thus it makes no sense to derive Vector (publicly) from Point (Liskov principle is violated!). Your Vector just inherited the setPos() member function which now can be called on it. What would it mean? A mathematical vector either does not have any position, or maybe it has two of them (start and end), if that's what you want to describe. IOW, there is no need to abuse inheritance just to avoid code replication. There are other ways to deal with code replication, starting from extracting the code into a separate ordinary function. hth Paavo |
| JiiPee <no@notvalid.com>: Dec 12 07:02PM On 12/12/2014 16:53, Paavo Helde wrote: >> { > As you just said, Vector is not a Point. Thus it makes no sense to derive > Vector (publicly) from Point (Liskov principle is violated!). true. Vector is not a type of point. > IOW, there is no need to abuse inheritance just to avoid code > replication. There are other ways to deal with code replication, starting > from extracting the code into a separate ordinary function. good idea. I will actually now think of doing this , might be best. But there are a lot of functions doing the same thing so I really want to re-use them. but this function thing might be a solution... |
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