Note: I already checked msdn, it doesn't address my actual question, see below.
I'm trying to use the obsolete attribute on a (obviously obsolete) constructor in one of my classes. Here's the scenario:
I want to be able to force the developer to update to the new constructor without affecting already existing and deployed code. This way I can deploy my code to production just fine, but from a developers perspective, whenever they go into their code, instead of just getting a "warning" which I'm sure they'll just ignore, I want them to get a compile error because the status quo is no longer ok.
So my question is, will this affect only developers, or all calling apps, or do I have the whole thing wrong?
sample code:
public class MyClass
{
private string _userID; //new code
[Obsolete("This constructor is obsolete, please use other constructor.", true)]
public MyClass()
{
_userID = ""; //defaulting to empty string for all those using this constructor
}
public MyClass(string userID)
{
_userID = userID; //this is why they need to use this constructor
}
}
Any and all help will be appreciated, thanks in advance!
Yes, this primarily affects the compiler - any pre-built code won't be affected... unless that code explicitly checks for this attribute. For example, some serialization code (XmlSerializer, IIRC) checks for this - so it might not be entirely side-effect free... but in principal existing code won't usually be affected until they try to compile next.
Of course, if you are using this code from something that uses dynamic compilation (for example ASP.NET without pre-compile) then all bets are off.
The attribute is only an instruction to the compiler. Already existing binaries can still use the constructor.
So my question is, will this affect only developers, or all calling apps, or do I have the whole thing wrong?
This will only be used at compile time, by the compiler. It will not affect applications which have already been deployed.
As such, this will have the behavior you are trying to accomplish.
This is what [Obsolete] already does, no extra help is needed. It is not a compile time warning, it generates an error:
error CS0619: 'ConsoleApplication1.MyClass.MyClass()' is obsolete:
'This constructor is obsolete, please use other constructor.'
Related
I have a huge code base and I recently made a change where I changed the type of a parameter from String to a custom class. On the next compile I got all the areas where the impact was, but areas where the input type was of type Object failed. for e.g.
String str = "32"
int i = Convert.ToInt32(str)
Now I have changed String to a new custom type lets say MyCustomClass I would now want following code to fail on next compile
MyCustomClass str = new MyCustomClass("32")
int i = Convert.ToInt32(str)
but it won't as Convert.ToInt32 also accepts type Object. Is there some way I can make a change in MyCustomClass that it's not considered Object anymore.
Please note: Convert.ToInt32 is only used for sample I have many more such functions, so please focus your suggestion/answer to question asked.
Override ToString() and IConvertible
You said in the comments that your intentions are to find places where your object, which had previously been treated as a string, and are now being treated as an object.
In these situations typically, the third-party code would call .ToString() on your object to get something which it can use.
So, Convert.ToInt32(str) is equivalent to Convert.ToInt32(str.ToString()).
If you implement ToString() and IConvertible to return whatever your old version of str looked like then it should continue to work in the same way as the old version.
Probably.
Sorry I know that is not the 100% perfect compile time answer you were looking for, but I think you also know very well that your MyCustomClass will always be considered object.
Possible compile time answer:
Write a tool which uses reflection to iterate over every class/struct/interface in every system/third-party DLL.
Output a load of CS files which contain all these same classes, but just throw NotImplementedException.
(T4 could help you do this)
Compile these classes into dummy.dll
Your .csproj now references only this one dummy.dll, instead of the real dlls.
Your project should compile fine against the dummy dll.
Look at your dummy.cs files and delete any use of object.
Re-compile... and suddenly you get a load of compile time errors showing you anywhere you are using an object.
Impliment an implicit cast from MyCustomClass to String.
public static implicit operator string(MyCustomClass str)
{
return "Legacy respresentation of str";
}
This allows the complier the choice of choosing ToInt32(Object) or ToInt32(String), and I bet it favours the later.
This way all your existing function calls will remain the same so you wont have to be concerned about third party implentation details.
(Sorry, I am not at a computer right now so I can`t test that my assumtion is correct. If you do test this, be sure to consider extension methods, as they can affect the conpilers desision making in unexpected ways)
Here is a piece of code:
IUser user = managerUser.GetUserById(UserId);
if ( user==null )
throw new Exception(...);
Quote quote = new Quote(user.FullName, user.Email);
Everything is fine here. But if I replace "if" line with the following one:
ComponentException<MyUserManagerException>.FailIfTrue(user == null, "Can't find user with Id=" + UserId);
where function implementation is following:
public abstract class ComponentException<T> : ComponentException
where T : ComponentException, new()
{
public static void FailIfTrue(bool expression, string message)
{
if (expression)
{
T t = new T();
t.SetErrorMessage(message);
throw t;
}
}
//...
}
Then ReSharper generates me a warning: Possible 'System.NullReferenceException' pointing on 1st usage of 'user' object.
Q1. Why it generates such exception? As far as I see if user==null then exception will be generated and execution will never reach the usage point.
Q2. How to remove that warning? Please note:
1. I don't want to suppress this warning with comments (I will have a lot of similar pieces and don't want to transform my source code in 'commented garbage);
2. I don't want to changes ReSharper settings to change this problem from warning to 'suggestion' of 'hint'.
Thanks.
Any thoughts are welcome!
P.S. I am using resharper 5.1, MVSV 2008, C#
Resharper only looks at the current method for its analysis, and does not recursively analyse other methods you call.
You can however direct Resharper a bit and give it meta-information about certain methods. It knows for example about "Assert.IsNotNull(a)", and will take that information into account for the analysis. It is possible to make an external annotations file for Resharper and give it extra information about a certain library to make its analysis better. Maybe this might offer a way to solve your problem.
More information can be found here.
An example showing how it's used for the library Microsoft.Contracts can be found here.
A new answer in old post...
Here a little sample of my code regarding how to use CodeContract via ContractAnnotation with Resharper:
[ContractAnnotation("value:null=>true")]
public static bool IsNullOrEmpty(this string value)
{
return string.IsNullOrEmpty(value);
}
It is very simple...if u find the breadcrumb in the wood. You can check other cases too.
Have a nice day
Q1: Because Resharper doesn't do path analysing. It just sees a possible null reference and flags that.
Q2: You can't without doing either of what you provided already.
You do know (or expect) that this code will throw an exception if there is a null reference:
ComponentException<MyUserManagerException>.FailIfTrue([...]);
However, since there is no contract specifying this, ReSharper has to assume that this is just a normal method call which may return without throwing any exception in any case.
Make this method implement the ReSharper contract, or as a simple workaround (which only affects debug mode, therefore no performance penalty for release mode), just after the FailIfTrue call:
Debug.Assert(user != null);
That will get rid of the warning, and as an added bonus do a runtime check in debug mode to ensure that the condition assumed by you after calling FailIfTrue is indeed met.
This is caused by the Resharper engine. These "possible NullReferenceException" happen because someone (probably at Resharper) has declared/configured somewhere an annotation on the method.
Here is how it works: ReSharper NullReferenceException Analysis and Its Contracts
Unfortunately, sometimes, these useful annotation are just wrong.
When you detect an error, you should report it to JetBrains and they will update the annotations on the next release. They're used to this.
Meanwhile, you can try to fix it by yourself. Read the article for more :)
Please check if you have any user==null if check above the given code. If there is, then ReSharper thinks that the variable "can be null" so recommends you to use a check/assert before referencing it. In some cases, that's the only way ReSharper can guess whether a variable can or cannot be null.
I am working on a c# library, so we are concerned with breaking backwards compatibility, but I was wondering is it possible to change just the name of a parameter and maintain backwards compatibility because of the ability to use named parameters? An example of what I am trying to do is below
[Obsolete("use ChangeSpecificFoo(SpecificFoo specificFoo)")]
public void ChangeSpecificFoo(SpecificFoo foo)
{
_specificFoo = foo;
}
//Compile error ... already defines a member called 'ChangeSpecificFoo' with the same parameter types
public void ChangeSpecificFoo(SpecificFoo specificFoo)
{
_specificFoo = specificFoo;
}
Just changing the parameter name runs the potential risk of breaking backwards compatibility because someone could be calling the method using named parameters like ChangeSpecificFoo(foo: someSpecificFoo) , but we can't deprecate the method by adding a new method with the correct parameter name because parameter names are not included in the method signature, so the compiler sees it as a duplicate.
Is there any way around this? The only alternatives I see are changing the method name so it is not a duplicate and then deprecating the old method, or waiting until we add or remove parameters from the parameter list and changing the parameter names then(this may never happen because the method is pretty stable), or just make the change and fix any breaks that we may have from code using this library as we find them.
My first inclination for this is simple: DON'T. The name of your parameter is irrelevant outside of the method body. You're right to consider people calling it out by name, and therefore potentially breaking it. However, just changing the name of the parameter gives no real benefit.
The only possible reason for changing the name is to redefine what the method does because the old name leads to confusion. In that case, the name of the method should also be changed in order to not introduce another form of confusion. (The fact that the method signatures are identical is the first and more important reason to not change parameter names. However, this is to potentially explain why you might want to.)
If however, you are still adamant about keeping the same method signature, but altering the name, you could do this. (Again, I'm strongly recommending you either don't change it at all, or rename the method as well to continue to eliminate confusion.)
One way around this would be to have the method with both parameters, but make the second optional. Have that last parameter use the old name, and then assign it over within the method.
I would also HIGHLY recommend logging any uses of the named parameter, to see if your concern is valid about people calling it as a named parameter.
public void ChangeSpecificFoo(SpecificFoo specificFoo = null, SpecificFoo foo = null)
{
if (foo != null && specificFoo == null)
{
// Add any other details you can, especially
// to figure out who is calling this.
Log("Someone used a name parameter!!");
}
_specificFoo = specificFoo ?? foo;
}
As Dmitry Bychenko pointed out in the comments, this will not stop anyone from calling this method like so: ChangeSpecificFoo(null, new SpecificFoo()), which will trigger a logging.
His observation introduces another reason why this is a bad idea: You're now introducing ANOTHER way for people to "incorrectly" call your method. Therefore, I'll repeat my advice from the top of my answer: DON'T do this, unless you really really really need to change that parameter name.
Lets say I got a boolean IsValid property on my object.
I would like to create a method, and ensure that IsValid isn't changed after calling it, whether it was true or false before the call.
Is there a support for such thing?
For that purpose the [Pure] Attribute has been added to the System.Diagnostic.Contracts Namespace. See here for further explanation. However you cannot prevent a single property from being changed. The method is not allowed to change the object state at all (like the C++ const).
EDIT: Unfortunately the Pure attribute does not work with the current tools. I implemented a test with the following code, no error message either at static nor at runtime type checking:
public class Test
{
private int x = 0;
[Pure]
public void Foo()
{
x++;
}
}
Regarding to the documentation of Pure checks will be supported 'in the future'. Whenever that is ("The Code Contracts team is working heavy on that, thus to come up with a purity checker in a future release.").
I have been using the attribute in the believe it works properly. The documentation says that all methods called within a contract must be declared as pure. It doesn't say whether that's checked or not.
So the answer to your question is: There is no current support for this, but may be in the future.
I haven't tried it myself, but according to the MSDN Contract.OldValue might help to check that a single property value has not changed:
public bool IsValid
{
get
{
...
}
}
public void SomeMethod()
{
Contract.Ensures(this.IsValid == Contract.OldValue(this.IsValid));
...
}
No, unfortunately c# doesn't provide a const logic such c++ does.
The only way to go about doing this is to control your code in such a way that you know it won't change. There is no specific code or syntax to control this otherwise (as in C++).
Is there a way to force the use of the this keyword in Visual Studio when referencing current instance members?
Example with a bug in the constructor:
class MyClass
{
public object Foo { get; set; }
public MyClass(object foo)
{
Foo = Foo; // this should of course be lowercase but it's easy to miss
}
}
This code will probably generate the infamous 'object reference not set to an instance of an object' exception somewhere later on.
How to make it work but still It's easy to miss:
class MyClass
{
public object Foo { get; set; }
public MyClass(object foo)
{
Foo = foo; // Valid syntax but unclear.
}
}
This is valid syntax but it's easy to miss.
The syntax I'd like visual studio enforce:
class MyClass
{
public object Foo { get; set; }
public MyClass(object foo)
{
this.Foo = foo; // this is "safe".
}
}
If this convention is enforced i would have to type this.Foo = this.Foo to create the same type of bug as in the first example.
I always use the this keyword anyway since it makes my life easier while switching between c# and other languages so there wouldn't be any disadvantages at all.
You can fix this simply by enabling "Treat warnings as errors":
Warning 2 Assignment made to same variable; did you mean to assign something else?
(CS1717 if you want to enable it just for this one)
The compiler already tells you about this; you should be reviewing the warnings (and aim for zero warnings).
Re the middle one being unclear:
Foo = foo;
I disagree - that is perfectly clear to me (unless you come from a VB background and have developed case-blindness).
No, you can't change the behaviour of the language like this. If you use ReSharper I believe you can tell it to flag up this sort of thing - it may not come up in the error list, but in the margin and in an "indicator light" for the overall file health.
I personally don't tend to lose too much sleep over this sort of thing, as it's usually obvious as soon as you test - I can only recall one scenario where it's really bitten me, which was when I ended up with a stack overflow (not exactly the same situation, but again a casing issue) within a type initializer, running on Windows Phone 7 - a mixture of difficult debug environments, basically.
You can use StyleCop to generate a warning if you do not prefix with this. You can get StyleCop to run as part of the build process by following these these instructions
StyleCop comes with a bunch of default rules, many of them terrible, but you can edit your rules file to make the most sense for your developers. You can also share the StyleCop file so changes are immediately replicated to all your developers.
Its a fairly nice solution, free, provided by Microsoft and if you come up with a suitable rule set then your developers will create much "neater" code. You can also create custom rules along the lines of "Methods shouldn't be too long" where you define the length. Plenty of things to play with.
Also I guess you could set warnings as errors, but if you do make sure your StyleCop settings are exactly as you want them.
You can create custom warnings and errors using FXCop\Visual Studio Code Analysis
You can use StyleCopAnalyzers, rule SA1101:
Cause:
A call to an instance member of the local class or a base class is not prefixed with 'this.', within a C# code file.
Then you can right click the rule in solution explorer and set it to error, now it will not compile if "this" is not used.