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Wtf? Goddamn Sh*t!
I would not expect that either.... I am a young player!!
Seulement, dans certains cas, n'est-ce pas, on n'entend guère que ce qu'on désire entendre et ce qui vous arrange le mieux... [^]
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Guirec Le Bars wrote: Wtf? Goddamn Sh*t!
That's almost exactly what I said when I realised what was going on!!!!
This was found in the middle of an MVVM framework that was causing me an issue. Good one, eh?
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Then you're not much elder than me
Seulement, dans certains cas, n'est-ce pas, on n'entend guère que ce qu'on désire entendre et ce qui vous arrange le mieux... [^]
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== resolves to System.Object.ReferenceEquals while contains determines equality by using the default equality comparer, as defined by the object's implementation.
People say nothing is impossible, but I do nothing every day.
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== will resolve to ReferenceEquals for reference types, and if there is no == operator override. For a value type (like bool) it will do a content equality.
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Quite right.
I referred to this specific case which of course wasn't obvious at all.
People say nothing is impossible, but I do nothing every day.
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That's exactly the opposite of what would seem reasonable to me.
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bool is a value type, so it is in the collection, because false == false.
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Not sure what is confusing you, the implementation of Contains obviously uses the Equals object override, so sucessfully finds arg1 and arg2. However, your list is a list of object (rather than a list of bool) so when it comes to using the equality operator instead of Equals, then you're comparing object references (not values!) and clearly arg1 is not arg2.
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I understand the difference and still I make that mistake occasionally. I guess my head isn't screwed on tightly enough.
People say nothing is impossible, but I do nothing every day.
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J4amieC wrote: Not sure what is confusing you,
Seriously? Honestly? you can't see the confusion?
Object1.equals(object2) == true;
When object1 and object2 are different objects that have the same value?
Assuming you didn't know what the objects were, are you telling me you honestly can't see a source of confusion?
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_Maxxx_ wrote: Object1.equals(object2) == true;
When object1 and object2 are different objects that have the same value?
Exactly, the point is I understand valuetype equality semantics from referencetype equality semantics. I agree they're somewhat confusing to new programmers.
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Except object isn't a valuetype
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object is not a value type but the thing you've stored in the object is a value type.
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If you get an email telling you that you can catch Swine Flu from tinned pork then just delete it. It's Spam.
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If I may be clear, I understand what is happening and why - the fact remains it is an inconsistency.
If each object had two booleans, would it act the same?
As an'outside observer' the behavior is inconsistent.
In the case where this came up, the framework was processing parameters passed to a constructor, and trying to find the best constructor to use based on the parameters.
The routine in question failed if two booleans were passed because e second was deemed to be the same parameter as the first when their values were equal.
Because this is a framework, and until now nobody had happened to write a constructor with multiple value types of the same type, and subsequently try to use it with those value types having the same value, nobody had noticed the issue.
If lit had been integers rather than booleans it would have been even more interesting - as the chances of the values also being equal wold be that much smaller.
So, I under stand what is happening, but I still regard this as an issue with the potential for causing larger problems I an application.
The fact that the Contains method works inconsistently depending on the contents of objects is the problem.
I ask 'does object a contain object b'
And I expect the answer to be yes or no - and not 'well, if it's an object containing only a value type, then the collection contains at least one similar Object where the value type has the same value, but if it's a reference type then that instance exists I the collection'
This means in principal that I need to know about the objects in any collection beforehand - which especially in a framework environment, I do not.
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Try this:
Sub Main()
Dim arg1 As Object = True
Dim arg2 As Object = True
Dim collection As New List(Of Object)() From { _
arg1 _
}
Dim first As Boolean = (collection.Contains(arg1))
Dim second As Boolean = (collection.Contains(arg2))
Console.WriteLine(String.Format("{0} {1}", first, second))
first = False
second = False
For i As Integer = 0 To collection.Count - 1
If collection(i) = arg1 Then
first = True
End If
If collection(i) = arg2 Then
second = True
End If
Next
Console.WriteLine(String.Format("{0} {1}", first, second))
Console.ReadKey()
End Sub
At least it's consistent.
People say nothing is impossible, but I do nothing every day.
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LOL - I am genuinely crying (with a little laughter and a lot of WTF!)
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Just pulling your leg a little bit.
Shorthand for ReferenceEquals in VB.Net is IS .
= is the shorthand for Equals .
So the VB code wasn't the same as your C# code.
I'v seen this error a few times in code that's been converted between VB and C#.
C# == is not the same as VB = , but oh so easy to miss if you only know one of the languages.
Should add that this is a standard error in all automatic converters I've tried.
People say nothing is impossible, but I do nothing every day.
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And then people complain about the confusing use of pointers and pointees in C/C++ ...
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Pointers and Pointees have a point, but in 95% of the cases the compiler would do a better job in handling it for you, and you can concentrate on the programming instead.
Just my 2c.
People say nothing is impossible, but I do nothing every day.
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I didn't intend to turn this into a C++ vs C# discussion, just point out that this specific case is just as confusing* as pointer use, which happens to be one of the stronger arguments against using C/C++.
I'm not saying this is a common problem in C#, just gloating over the realization that you cannot completely avoid the heritage.
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I we would make a list of confusing parts of programming languages, any language, we would run out of harddisk space pretty soon.
People say nothing is impossible, but I do nothing every day.
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_Maxxx_ wrote: If each object had two booleans, would it act the same?
Depends if it's a value type, and whether Equals is overridden.
_Maxxx_ wrote: The fact that the Contains method works inconsistently depending on the contents of objects is the problem.
It does not behave differently depending on the contents. It depends differently depending on the type. You can think of it like string interning: there is only one false so when you have two of them, they are always equal, both in value terms and in reference terms. I think this is true for all value types; it's certainly true for all basic types.
_Maxxx_ wrote: And I expect the answer to be yes or no - and not 'well, if it's an object containing only a value type, then the collection contains at least one similar Object where the value type has the same value, but if it's a reference type then that instance exists I the collection'
The answer is yes if there is an object in the collection for which Equals with the one you've passed returns true. That's what equality means, and it's usually much more useful than checking for reference equality. You can override == on custom types to make that check whatever you want. By default the behaviour is to check references for reference types and to check values for value types (or at least base types).
Choosing which constructor to use based on the values of parameters, instead of the types of parameters, is a WTF all to itself.
Edit: Equals, not ==. I always override both of these, and also !=, if I do either, so I get them mixed up sometimes.
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BobJanova wrote: Depends if it's a value type, and whether Equals is overridden.
Not sure I even follow you there. An object with two boolean properties is not a value type - or am I misunderstanding you?
BobJanova wrote: and it's usually much more useful than checking for reference equality.
I have to disagree there, and say it entirely depends on the context. If I want to check if two objects are the same object, i would like to be able to do so in a consistent manner, without having to check to see if the object is a value-type wrapper. similarly, if I want to check if the value of two objects are the same, I would expect to be able to use the same methods regardless as to whether the objects in question have booleans or Customers internally.
I reiterate - I understand exactly what is happening, and it is a trick for young players (hence the post). But I still think that there is an inherent (pun absolutely intended) discrepancy n the handling of boxed objects vs the handling of 'vanilla' objects.
BobJanova wrote: Choosing which constructor to use based on the values of parameters, instead of the types of parameters, is a WTF all to itself.
The AIM of the method in question was was to decide on the constructor based upon the TYPES of parameter vs TYPES of arguments.
The parameters were in a collection and the arguments in another.
1. For Each parameter in the constructor it is checking
2. For each argument in the collection
3. If THIS ARGUMENT is already in our output collection, continue
4. If this argument is of the same type (or subtype etc) as the current parameter, add it to the output collection
5. Next Argument
6. Next parameter
Line 3 is where the issue arises, because if there are two value arguments, and they both have the same runtime value, then this If is triggered and the argument ignored for the 2nd and subsequent parameter.
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