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I have access to a class structure, which I cannot modify, as follows:
Graphics
Circle
Line
etc.
Again, I cannot modify it! These all have individual properties such as Radius, FirstPoint, LastPoint, etc., as well as some common properties.
I want to create a method that accepts a Graphics object, and depending on the type of object, will run a ToJson method:
Graphics g = db.GetGraphic(123);
// Console.WriteLine(g.GetType()) prints "Circle"
// Should run some specific implementation for `Circle` type graphics, and
// have an overload for all types including Graphics
ToJson(g);
At first I imagined I could craftily overload the ToJson method:
ToJson(Graphics g) ...
ToJson(Circle g) ...
ToJson(Line g) ...
however this of course goes for the generic ToJson(Graphics) overload each time.
I'm sure I could do something like the following:
if (g is Circle) ...
if (g is Line) ...
if (g is Graphics) ...
or create a Dictionary to reduce the complexity for each type, but that doesn't feel like the best way of doing things
What I've considered
I've considered if there's some generic wrapper method I could use around each object (e.g., new JsonGraphics(g).ToJson()), but I do not want to have to perform any manual type checking myself.
I have looked at the double dispatch and visitor pattern, but I wasn't sure they met my requirements as they look like I have to modify these classes (or maybe I just didn't fully understand them), and (kinda obvious, however) generics are also basically out of the window as they require me to know in advance what type of Graphics object this is.
Two questions then:
Is there a better way to do this other than to use some Dictionary or something other if (g is Type)-like?
If I could modify the classes, how would the pattern look? This isn't possible in this case, but is double dispatch/visitor the best way to go in the case I could?
c# inheritance overloading visitor double-dispatch
asked Mar 27 at 14:40
Nick BullNick Bull
6,6663 gold badges16 silver badges27 bronze badges
|
show 9 more comments
I have access to a class structure, which I cannot modify, as follows:
Graphics
Circle
Line
etc.
Again, I cannot modify it! These all have individual properties such as Radius, FirstPoint, LastPoint, etc., as well as some common properties.
I want to create a method that accepts a Graphics object, and depending on the type of object, will run a ToJson method:
Graphics g = db.GetGraphic(123);
// Console.WriteLine(g.GetType()) prints "Circle"
// Should run some specific implementation for `Circle` type graphics, and
// have an overload for all types including Graphics
ToJson(g);
At first I imagined I could craftily overload the ToJson method:
ToJson(Graphics g) ...
ToJson(Circle g) ...
ToJson(Line g) ...
however this of course goes for the generic ToJson(Graphics) overload each time.
I'm sure I could do something like the following:
if (g is Circle) ...
if (g is Line) ...
if (g is Graphics) ...
or create a Dictionary to reduce the complexity for each type, but that doesn't feel like the best way of doing things
What I've considered
I've considered if there's some generic wrapper method I could use around each object (e.g., new JsonGraphics(g).ToJson()), but I do not want to have to perform any manual type checking myself.
I have looked at the double dispatch and visitor pattern, but I wasn't sure they met my requirements as they look like I have to modify these classes (or maybe I just didn't fully understand them), and (kinda obvious, however) generics are also basically out of the window as they require me to know in advance what type of Graphics object this is.
Two questions then:
Is there a better way to do this other than to use some Dictionary or something other if (g is Type)-like?
If I could modify the classes, how would the pattern look? This isn't possible in this case, but is double dispatch/visitor the best way to go in the case I could?
c# inheritance overloading visitor double-dispatch
asked Mar 27 at 14:40
Nick BullNick Bull
6,6663 gold badges16 silver badges27 bronze badges
If you could modify the types, you would add a virtual/abstract ToJson instance method and override as needed. A "rule engine" where you use reflection to find the right implementation of the ToJson code is probably the best way to go.
– Lasse Vågsæther Karlsen
Mar 27 at 14:42
So yes, a dictionary of type to delegate/object that implements this is probably what I would choose myself.
– Lasse Vågsæther Karlsen
Mar 27 at 14:43
Decorator pattern?
– Kenneth K.
Mar 27 at 14:43
1
As you note, to use the visitor pattern for double dispatch, you need the "visited" class to implement a method that calls the "visitor" class back on the appropriate method. I give a simple example here: ericlippert.com/2015/05/04/wizards-and-warriors-part-three You normally use the visitor pattern when you have a group of related objects, you have a variety of analysis or transformation passes you need to perform on those objects, and the exact details of each operation depend on the run-time type of both the visited and visitor objects.
– Eric Lippert
Mar 27 at 15:26
1
Thank you for your input Eric - I'll give that a read! 🙂
– Nick Bull
Mar 27 at 17:07
|
show 9 more comments
I have access to a class structure, which I cannot modify, as follows:
Graphics
Circle
Line
etc.
Again, I cannot modify it! These all have individual properties such as Radius, FirstPoint, LastPoint, etc., as well as some common properties.
I want to create a method that accepts a Graphics object, and depending on the type of object, will run a ToJson method:
Graphics g = db.GetGraphic(123);
// Console.WriteLine(g.GetType()) prints "Circle"
// Should run some specific implementation for `Circle` type graphics, and
// have an overload for all types including Graphics
ToJson(g);
At first I imagined I could craftily overload the ToJson method:
ToJson(Graphics g) ...
ToJson(Circle g) ...
ToJson(Line g) ...
however this of course goes for the generic ToJson(Graphics) overload each time.
I'm sure I could do something like the following:
if (g is Circle) ...
if (g is Line) ...
if (g is Graphics) ...
or create a Dictionary to reduce the complexity for each type, but that doesn't feel like the best way of doing things
What I've considered
I've considered if there's some generic wrapper method I could use around each object (e.g., new JsonGraphics(g).ToJson()), but I do not want to have to perform any manual type checking myself.
I have looked at the double dispatch and visitor pattern, but I wasn't sure they met my requirements as they look like I have to modify these classes (or maybe I just didn't fully understand them), and (kinda obvious, however) generics are also basically out of the window as they require me to know in advance what type of Graphics object this is.
Two questions then:
Is there a better way to do this other than to use some Dictionary or something other if (g is Type)-like?
If I could modify the classes, how would the pattern look? This isn't possible in this case, but is double dispatch/visitor the best way to go in the case I could?
c# inheritance overloading visitor double-dispatch
asked Mar 27 at 14:40
Nick BullNick Bull
6,6663 gold badges16 silver badges27 bronze badges
I have access to a class structure, which I cannot modify, as follows:
Graphics
Circle
Line
etc.
Again, I cannot modify it! These all have individual properties such as Radius, FirstPoint, LastPoint, etc., as well as some common properties.
I want to create a method that accepts a Graphics object, and depending on the type of object, will run a ToJson method:
Graphics g = db.GetGraphic(123);
// Console.WriteLine(g.GetType()) prints "Circle"
// Should run some specific implementation for `Circle` type graphics, and
// have an overload for all types including Graphics
ToJson(g);
At first I imagined I could craftily overload the ToJson method:
ToJson(Graphics g) ...
ToJson(Circle g) ...
ToJson(Line g) ...
however this of course goes for the generic ToJson(Graphics) overload each time.
I'm sure I could do something like the following:
if (g is Circle) ...
if (g is Line) ...
if (g is Graphics) ...
or create a Dictionary to reduce the complexity for each type, but that doesn't feel like the best way of doing things
What I've considered
I've considered if there's some generic wrapper method I could use around each object (e.g., new JsonGraphics(g).ToJson()), but I do not want to have to perform any manual type checking myself.
I have looked at the double dispatch and visitor pattern, but I wasn't sure they met my requirements as they look like I have to modify these classes (or maybe I just didn't fully understand them), and (kinda obvious, however) generics are also basically out of the window as they require me to know in advance what type of Graphics object this is.
Two questions then:
Is there a better way to do this other than to use some Dictionary or something other if (g is Type)-like?
If I could modify the classes, how would the pattern look? This isn't possible in this case, but is double dispatch/visitor the best way to go in the case I could?
c# inheritance overloading visitor double-dispatch
c# inheritance overloading visitor double-dispatch
asked Mar 27 at 14:40
Nick BullNick Bull
6,6663 gold badges16 silver badges27 bronze badges
asked Mar 27 at 14:40
Nick BullNick Bull
6,6663 gold badges16 silver badges27 bronze badges
edited Mar 27 at 14:42
Nick Bull
asked Mar 27 at 14:40
Nick BullNick Bull
6,6663 gold badges16 silver badges27 bronze badges
asked Mar 27 at 14:40
Nick BullNick Bull
6,6663 gold badges16 silver badges27 bronze badges
asked Mar 27 at 14:40
Nick BullNick Bull
6,6663 gold badges16 silver badges27 bronze badges
6,6663 gold badges16 silver badges27 bronze badges
If you could modify the types, you would add a virtual/abstract ToJson instance method and override as needed. A "rule engine" where you use reflection to find the right implementation of the ToJson code is probably the best way to go.
– Lasse Vågsæther Karlsen
Mar 27 at 14:42
So yes, a dictionary of type to delegate/object that implements this is probably what I would choose myself.
– Lasse Vågsæther Karlsen
Mar 27 at 14:43
Decorator pattern?
– Kenneth K.
Mar 27 at 14:43
1
As you note, to use the visitor pattern for double dispatch, you need the "visited" class to implement a method that calls the "visitor" class back on the appropriate method. I give a simple example here: ericlippert.com/2015/05/04/wizards-and-warriors-part-three You normally use the visitor pattern when you have a group of related objects, you have a variety of analysis or transformation passes you need to perform on those objects, and the exact details of each operation depend on the run-time type of both the visited and visitor objects.
– Eric Lippert
Mar 27 at 15:26
1
Thank you for your input Eric - I'll give that a read! 🙂
– Nick Bull
Mar 27 at 17:07
|
show 9 more comments
If you could modify the types, you would add a virtual/abstract ToJson instance method and override as needed. A "rule engine" where you use reflection to find the right implementation of the ToJson code is probably the best way to go.
– Lasse Vågsæther Karlsen
Mar 27 at 14:42
So yes, a dictionary of type to delegate/object that implements this is probably what I would choose myself.
– Lasse Vågsæther Karlsen
Mar 27 at 14:43
Decorator pattern?
– Kenneth K.
Mar 27 at 14:43
1
As you note, to use the visitor pattern for double dispatch, you need the "visited" class to implement a method that calls the "visitor" class back on the appropriate method. I give a simple example here: ericlippert.com/2015/05/04/wizards-and-warriors-part-three You normally use the visitor pattern when you have a group of related objects, you have a variety of analysis or transformation passes you need to perform on those objects, and the exact details of each operation depend on the run-time type of both the visited and visitor objects.
– Eric Lippert
Mar 27 at 15:26
1
Thank you for your input Eric - I'll give that a read! 🙂
– Nick Bull
Mar 27 at 17:07
If you could modify the types, you would add a virtual/abstract ToJson instance method and override as needed. A "rule engine" where you use reflection to find the right implementation of the ToJson code is probably the best way to go.
– Lasse Vågsæther Karlsen
Mar 27 at 14:42
If you could modify the types, you would add a virtual/abstract ToJson instance method and override as needed. A "rule engine" where you use reflection to find the right implementation of the ToJson code is probably the best way to go.
– Lasse Vågsæther Karlsen
Mar 27 at 14:42
So yes, a dictionary of type to delegate/object that implements this is probably what I would choose myself.
– Lasse Vågsæther Karlsen
Mar 27 at 14:43
So yes, a dictionary of type to delegate/object that implements this is probably what I would choose myself.
– Lasse Vågsæther Karlsen
Mar 27 at 14:43
Decorator pattern?
– Kenneth K.
Mar 27 at 14:43
Decorator pattern?
– Kenneth K.
Mar 27 at 14:43
1
1
As you note, to use the visitor pattern for double dispatch, you need the "visited" class to implement a method that calls the "visitor" class back on the appropriate method. I give a simple example here: ericlippert.com/2015/05/04/wizards-and-warriors-part-three You normally use the visitor pattern when you have a group of related objects, you have a variety of analysis or transformation passes you need to perform on those objects, and the exact details of each operation depend on the run-time type of both the visited and visitor objects.
– Eric Lippert
Mar 27 at 15:26
As you note, to use the visitor pattern for double dispatch, you need the "visited" class to implement a method that calls the "visitor" class back on the appropriate method. I give a simple example here: ericlippert.com/2015/05/04/wizards-and-warriors-part-three You normally use the visitor pattern when you have a group of related objects, you have a variety of analysis or transformation passes you need to perform on those objects, and the exact details of each operation depend on the run-time type of both the visited and visitor objects.
– Eric Lippert
Mar 27 at 15:26
1
1
Thank you for your input Eric - I'll give that a read! 🙂
– Nick Bull
Mar 27 at 17:07
Thank you for your input Eric - I'll give that a read! 🙂
– Nick Bull
Mar 27 at 17:07
|
show 9 more comments
1 Answer
1
active
oldest
votes
Without being able to modify the base class, or have access to the concrete type before it's turned into a generic Graphics type, unfortunately I don't think there's anything you can do except inspect the runtime type of the Graphics object.
You can use a switch statement (since C# 7.0), which is slightly cleaner than your if chain:
switch (g)
case Circle circle: ... break;
case Line line: ... break;
default: /* Oh no! */ break;
Personally I don't see much advantage in using a Dictionary over a switch statement like this - both can be put away into a little self-contained method (and so reduce the amount of violation of the open/close principle), but the switch will be significantly cheaper.
You can also use dynamic, which causes the runtime to do late binding:
dynamic d = g;
ToJson(d); // Picks the right ToJson overload corresponding to the runtime type of 'd'
... although, dynamic has a fairly large runtime cost, and is generally considered smell.
answered Mar 27 at 14:47
canton7canton7
7,7351 gold badge19 silver badges31 bronze badges
Theswitchis using some pattern matching? I wasn't aware switch statements in C# could do that! :)
– Nick Bull
Mar 27 at 14:48
1
@Nick Yes, since C# 7.0
– canton7
Mar 27 at 14:49
Oh man, it's been a while. I last used C# when it was at 5.0, I feel old
– Nick Bull
Mar 27 at 14:52
1
To be fair, nothing ground-breaking has happened since 5.0 (apart from Roslyn) - it's been lots of little improvements. C# 8 is going to be ground-breaking again, though
– canton7
Mar 27 at 14:54
add a comment |
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Without being able to modify the base class, or have access to the concrete type before it's turned into a generic Graphics type, unfortunately I don't think there's anything you can do except inspect the runtime type of the Graphics object.
You can use a switch statement (since C# 7.0), which is slightly cleaner than your if chain:
switch (g)
case Circle circle: ... break;
case Line line: ... break;
default: /* Oh no! */ break;
Personally I don't see much advantage in using a Dictionary over a switch statement like this - both can be put away into a little self-contained method (and so reduce the amount of violation of the open/close principle), but the switch will be significantly cheaper.
You can also use dynamic, which causes the runtime to do late binding:
dynamic d = g;
ToJson(d); // Picks the right ToJson overload corresponding to the runtime type of 'd'
... although, dynamic has a fairly large runtime cost, and is generally considered smell.
answered Mar 27 at 14:47
canton7canton7
7,7351 gold badge19 silver badges31 bronze badges
Theswitchis using some pattern matching? I wasn't aware switch statements in C# could do that! :)
– Nick Bull
Mar 27 at 14:48
1
@Nick Yes, since C# 7.0
– canton7
Mar 27 at 14:49
Oh man, it's been a while. I last used C# when it was at 5.0, I feel old
– Nick Bull
Mar 27 at 14:52
1
To be fair, nothing ground-breaking has happened since 5.0 (apart from Roslyn) - it's been lots of little improvements. C# 8 is going to be ground-breaking again, though
– canton7
Mar 27 at 14:54
add a comment |
Without being able to modify the base class, or have access to the concrete type before it's turned into a generic Graphics type, unfortunately I don't think there's anything you can do except inspect the runtime type of the Graphics object.
You can use a switch statement (since C# 7.0), which is slightly cleaner than your if chain:
switch (g)
case Circle circle: ... break;
case Line line: ... break;
default: /* Oh no! */ break;
Personally I don't see much advantage in using a Dictionary over a switch statement like this - both can be put away into a little self-contained method (and so reduce the amount of violation of the open/close principle), but the switch will be significantly cheaper.
You can also use dynamic, which causes the runtime to do late binding:
dynamic d = g;
ToJson(d); // Picks the right ToJson overload corresponding to the runtime type of 'd'
... although, dynamic has a fairly large runtime cost, and is generally considered smell.
answered Mar 27 at 14:47
canton7canton7
7,7351 gold badge19 silver badges31 bronze badges
Theswitchis using some pattern matching? I wasn't aware switch statements in C# could do that! :)
– Nick Bull
Mar 27 at 14:48
1
@Nick Yes, since C# 7.0
– canton7
Mar 27 at 14:49
Oh man, it's been a while. I last used C# when it was at 5.0, I feel old
– Nick Bull
Mar 27 at 14:52
1
To be fair, nothing ground-breaking has happened since 5.0 (apart from Roslyn) - it's been lots of little improvements. C# 8 is going to be ground-breaking again, though
– canton7
Mar 27 at 14:54
add a comment |
Without being able to modify the base class, or have access to the concrete type before it's turned into a generic Graphics type, unfortunately I don't think there's anything you can do except inspect the runtime type of the Graphics object.
You can use a switch statement (since C# 7.0), which is slightly cleaner than your if chain:
switch (g)
case Circle circle: ... break;
case Line line: ... break;
default: /* Oh no! */ break;
Personally I don't see much advantage in using a Dictionary over a switch statement like this - both can be put away into a little self-contained method (and so reduce the amount of violation of the open/close principle), but the switch will be significantly cheaper.
You can also use dynamic, which causes the runtime to do late binding:
dynamic d = g;
ToJson(d); // Picks the right ToJson overload corresponding to the runtime type of 'd'
... although, dynamic has a fairly large runtime cost, and is generally considered smell.
answered Mar 27 at 14:47
canton7canton7
7,7351 gold badge19 silver badges31 bronze badges
Without being able to modify the base class, or have access to the concrete type before it's turned into a generic Graphics type, unfortunately I don't think there's anything you can do except inspect the runtime type of the Graphics object.
You can use a switch statement (since C# 7.0), which is slightly cleaner than your if chain:
switch (g)
case Circle circle: ... break;
case Line line: ... break;
default: /* Oh no! */ break;
Personally I don't see much advantage in using a Dictionary over a switch statement like this - both can be put away into a little self-contained method (and so reduce the amount of violation of the open/close principle), but the switch will be significantly cheaper.
You can also use dynamic, which causes the runtime to do late binding:
dynamic d = g;
ToJson(d); // Picks the right ToJson overload corresponding to the runtime type of 'd'
... although, dynamic has a fairly large runtime cost, and is generally considered smell.
answered Mar 27 at 14:47
canton7canton7
7,7351 gold badge19 silver badges31 bronze badges
edited Mar 27 at 15:05
answered Mar 27 at 14:47
canton7canton7
7,7351 gold badge19 silver badges31 bronze badges
answered Mar 27 at 14:47
canton7canton7
7,7351 gold badge19 silver badges31 bronze badges
answered Mar 27 at 14:47
canton7canton7
7,7351 gold badge19 silver badges31 bronze badges
7,7351 gold badge19 silver badges31 bronze badges
Theswitchis using some pattern matching? I wasn't aware switch statements in C# could do that! :)
– Nick Bull
Mar 27 at 14:48
1
@Nick Yes, since C# 7.0
– canton7
Mar 27 at 14:49
Oh man, it's been a while. I last used C# when it was at 5.0, I feel old
– Nick Bull
Mar 27 at 14:52
1
To be fair, nothing ground-breaking has happened since 5.0 (apart from Roslyn) - it's been lots of little improvements. C# 8 is going to be ground-breaking again, though
– canton7
Mar 27 at 14:54
add a comment |
Theswitchis using some pattern matching? I wasn't aware switch statements in C# could do that! :)
– Nick Bull
Mar 27 at 14:48
1
@Nick Yes, since C# 7.0
– canton7
Mar 27 at 14:49
Oh man, it's been a while. I last used C# when it was at 5.0, I feel old
– Nick Bull
Mar 27 at 14:52
1
To be fair, nothing ground-breaking has happened since 5.0 (apart from Roslyn) - it's been lots of little improvements. C# 8 is going to be ground-breaking again, though
– canton7
Mar 27 at 14:54
The
switch is using some pattern matching? I wasn't aware switch statements in C# could do that! :)– Nick Bull
Mar 27 at 14:48
The
switch is using some pattern matching? I wasn't aware switch statements in C# could do that! :)– Nick Bull
Mar 27 at 14:48
1
1
@Nick Yes, since C# 7.0
– canton7
Mar 27 at 14:49
@Nick Yes, since C# 7.0
– canton7
Mar 27 at 14:49
Oh man, it's been a while. I last used C# when it was at 5.0, I feel old
– Nick Bull
Mar 27 at 14:52
Oh man, it's been a while. I last used C# when it was at 5.0, I feel old
– Nick Bull
Mar 27 at 14:52
1
1
To be fair, nothing ground-breaking has happened since 5.0 (apart from Roslyn) - it's been lots of little improvements. C# 8 is going to be ground-breaking again, though
– canton7
Mar 27 at 14:54
To be fair, nothing ground-breaking has happened since 5.0 (apart from Roslyn) - it's been lots of little improvements. C# 8 is going to be ground-breaking again, though
– canton7
Mar 27 at 14:54
add a comment |
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If you could modify the types, you would add a virtual/abstract ToJson instance method and override as needed. A "rule engine" where you use reflection to find the right implementation of the ToJson code is probably the best way to go.
– Lasse Vågsæther Karlsen
Mar 27 at 14:42
So yes, a dictionary of type to delegate/object that implements this is probably what I would choose myself.
– Lasse Vågsæther Karlsen
Mar 27 at 14:43
Decorator pattern?
– Kenneth K.
Mar 27 at 14:43
1
As you note, to use the visitor pattern for double dispatch, you need the "visited" class to implement a method that calls the "visitor" class back on the appropriate method. I give a simple example here: ericlippert.com/2015/05/04/wizards-and-warriors-part-three You normally use the visitor pattern when you have a group of related objects, you have a variety of analysis or transformation passes you need to perform on those objects, and the exact details of each operation depend on the run-time type of both the visited and visitor objects.
– Eric Lippert
Mar 27 at 15:26
1
Thank you for your input Eric - I'll give that a read! 🙂
– Nick Bull
Mar 27 at 17:07