I would like to be able to keep a C# API the same as it is now, but simply deprecate one of the parameters in a method call. Is it possible to do so, or do I need to create a new method without the parameter and mark the original one as Obsolete?
Short answer:
You will need to create a new nethod with the new signature, and mark the current as obsolete.
Longer answer
What you want to avoid at all cost is a code break! Then, particularly in a company framework, you want to advertise that your method will no longer be supported, for example, but you do not want to be responsible for depending solutions to crash because of an architecture or design decision or your side, right?
The ObsoleteAttribute class will do the trick for you.
Once a class member marked as obsolete, a warning will be raised on the client-side, the ones who use your framework, to continue that way, or even one of your colleague under the same project.
public class MyClass {
[Obsolete("This method should no longer be used, please use MyNewMethod() instead.")]
public void MyMethod(string name, long phoneNumber, long faxNumber) {
}
public void MyNewMethod(string name, long phoneNumber, long faxNumber, string email) {
}
}
This will advertise that MyMethod is no longer supported throughout your code users.
After a certain period of time, reasonable enough to allow everyone to change his/her code, you may tell this attribute to throw an error message when your obsolete method is still used in the code.
public class MyClass {
[Obsolete("This method should no longer be used, please use MyNewMethod() instead.", true)]
public void MyMethod(string name, long phoneNumber, long faxNumber) {
}
public void MyNewMethod(string name, long phoneNumber, long faxNumber, string email) {
}
}
By setting the second ObsoleteAttribute class constructor parameter to true, you tel the compiler to advertise the use of this method as an error.
After some time only, you can completely remove your method from your code to clean it up a little. This is part of the refactoring methods encouraged by the Agile Software Development methodology.
Does this help?
Yes, I think the only way is to create a new method without the parameter and mark the original one with ObsoleteAttribute.
With the Obsolete attribute:
[Obsolete("Please use void AnotherMethod() instead", false)]
void SomeMethod(Int32 data){
}
The Boolean in the attribute tells the compiler to generate a warning, if you change it to true the compiler will generate an error. See here for the documentation on it.
Yes. You can only mark types and members of types as obsolete, not individual parameters. You could, however, overload the method, thereby keeping the same name and mark the old one as obsolete:
class Act
{
[Obsolete("DoSomething(int, int) is obsolete", false /*warn only*/)]
public void DoSomething(int i, int j)
{
}
public void DoSomething(int i)
{
}
}
I think it would be best to create a new method.
What do you mean by making the parameter obsolete? Does this depend on a specific value for that argument? When you call a method, you always have to specify the argument anyway.
Related
I know the CallerMemberName-attribute, which replaces the null parameter with, for example, the property name you are calling the method from.
This is very useful for things like PropertyChanged-Notifications. Currently we have a different scenario, where we would like to have a parameter-attribute which replaces the null parameter with the method name you're calling.
Generally speaking, is it possible to do something like this?
To be honest, I havent dealt much with custom attribute yet, but in our case, it would be kinda interesting to have something like this.
Is there any helpful Information I can start with?
There is no such attribute, but you could use C# 6 nameof operator:
public void SomeMethod ()
{
Console.WriteLine(nameof(SomeMethod));
}
Of course this does not dynamically and automatically inserts the name of the method you are in, but requires you to have an actual reference to the method. However, it supports full IntelliSense and will also update automatically when you refactor the method name. And the name is inserted at compile time, so you don’t get any performance downside.
If you wanted to place this code in a more central place, like you do with e.g. INPC implementations in base view models, then your idea is a bit flawed anyway. If you had a common method you call to figure out the method name you’re in, then it would always report the method name of the common method:
public void SomeMethod ()
{
Console.WriteLine(GetMethodName());
}
// assuming that a CallingMemberNameAttribute existed
public string GetMethodName([CallingMemberName] string callingMember = null)
{
return callingMember; // would be always "GetMethodName"
}
But instead, you could use the CallerMemberNameAttribute here again, which will then correctly get the method name calling the GetMethodName function:
public void SomeMethod ()
{
Console.WriteLine(GetMethodName());
}
public string GetMethodName([CallerMemberNamed] string callerMember = null)
{
return callerMember;
}
Sorry if the question sounds confusing. What I mean is that if I have a class that has a method that does a bunch of calculations and then returns a value, I can either make that method public (which gives my other classes access), or I can make it private and make a public get method.
Something like this:
public publicmethod{
return privatemethod();
}
private privatemethod{
//do stuff
return value;
}
Is this a futile exercise or does it provide additional program security?
Well, there is no additional security here. However, such a usage can sometimes make sense.
For example, the private and public method may have different semantics.
// base class
public virtual BuyFood()
{
BuyPizza();
BuyCoke();
}
private void BuyPizza()
{
// ...
}
// derived class
public override void BuyFood()
{
BuyChopSuey();
}
private void BuyChopSuey()
{
// ...
}
So your implementation is just calling to a private method -- but what is important, you expose the semantics: your BuyFood operation is just BuyChopSuey(). Your code says: "in this class, buying food is just buying chop suey" in a clear way. You are able to add BuyTsingtaoBeer() into BuyFood() any time without changing the semantics of the both methods.
It is completely redundant. It does not provide anything except another name for the same thing and another indirection for readers to follow. Simply make a single implementation, and make it public. On the same note, getX() { return x; } setX(T newX) { x = newX; } does not encapsulate anything, at best it's future-proofing.
You may end up implementing a particular function required by an interface in a single line, largely delegating to (possibly private) methods which exist for other good reasons. This is different, and more justified (but again, if it's only return someMethod(); you should probably abolish the private implementation and assume the common name). A particular case if when you need two implement two methods which do the same thing (e.g. from separate interfaces).
I think either way is fine, it's more a matter of style assuming the method doesn't change the state of the class. If you have a class that has a bunch of properties and very few methods, it probably makes more sense to define another property. If you have a lot of methods in the class but few properties, then a method is more consistent with your overall class design.
If the method changes a bunch of other class variables than I'd expose it as a public method instead of a property.
I don't think either way, property or method, is necessarily more secure. It depends on what checks you do - is the caller allowed to perform the calculation? Are all variables used in the calculations within acceptable ranges? Etc. All of these checks can be performed whether you are using a property or a method.
Well, actually the question is What code do I want to be able to call this method?
Any code in general, even from other assemblies? Make the method public.
Any code from the same assembly? Make it internal.
Only code from this class? Make it private.
Having a private method directly aliased to a public method only makes the private method callable from the outside, which contradicts its private status.
If the method only does some calculation and doesn't use or change anything in the object, make it a public static method:
public static CalculationMethod(int input) {
//do stuff
return value;
}
That way any code can use the method without having the create an instance of the class:
int result = ClassName.CalculationMethod(42);
Instead of public consider internal, which would give access only to code in the same assembly.
I have an interface IKey which I want to have a method which will return the key as a string. We looked at having a method like this:
String GetAsString();
which would return the string representation, but would have liked to be able to declare ToString() again in the interface to force implementers to implement it, but it doesn't force them to as they have an implementation inherited from Object. This was suggested:
public interface IKey
{
string ToString(string dummyParameter=null);
}
this forces an implementation of the method in any implementing class, but due to the way that optional parameters work callers do not need to provide a value for this, and you ensure that any calls to the ToString() method on objects which are either cast as the interface IKey or the implementing class will always call the class implementation and not the Object implementation.
In the implementations we can just ignore the dummyParameter and return what we want, safe in the knowledge that calling ToString() will always actually call ToString(null).
Now this feels wrong all over to me, but at the same time it does have something quite nice about it. It is almost exactly the same as having a method GetAsString() as this could only be called on the IKey interface and derived classes except that it looks like the more natural ToString() method that we want to use and that we are able to force the implementing of in the child class.
Having said that the dummy parameter which is not used feels wrong.
So is this horrendous? Or great?
And is this question appropriate for SO or should it be on Programmers?
Examples
public class Key :IKey
{
public string ToString(string abc = null)
{
return "100";
}
}
Key key = new Key ();
Trace.WriteLine (key.ToString());
Trace.WriteLine (key.ToString(null));
Trace.WriteLine (key.ToString("ac"));
Trace.WriteLine (((object)key).ToString());
output:
100
100
100
Blah.Tests.Key
It sounds like you're using an interface where you should be using an abstract class. The class below explicitly requires descendants to have implemented ToString.
abstract class X
{
public abstract override string ToString();
}
From my point of view such ToString() method in a custom interface slightly messed up things because a custom interface exposed a method with standard and well known name ToString().
I prefer something more straightforward and obvious like:
string KeyText { get; }
OR method
string ConvertKeyToString();
Another answer already suggests the abstract class, which I think is the best option for this.
The idea of adding a ToString with a default parameter to the interface doesn't work too well in practive. The overload resolution will find the ToString without parameters when called without parameters (which, I must say, seems intuitive). Consider the output of this program:
void Main()
{
Console.WriteLine(new Key().ToString());
}
public interface IKey
{
string ToString(string dummy = null);
}
class Key : IKey
{
public string ToString(string dummy)
{
return "myspecialKey";
}
}
This outputs the object.ToString() implementation. Therefore, if you are restricted to use an interface, I would name the method something else than ToString().
Re-purposing
(IMO) -ToString() already has a very well-defined purpose and meaning. It may be convenient for you to hijack it based on the name, but by saying it's required you're re-purposing something that you shouldn't.
The answer is to have your own separate method, the initial idea. Anything else means all the .NET documentation about ToString() becomes 'wrong'.
E.g. the Tag property being an object on many UI controls. It could be that you want to 'tag' controls in some kind of control gallery. Just because the name fits, and the type fits, doesn't mean the meaning is the same and you can grab hold of it and re-purpose it.
Naming
I would also suggest considering changing your interface name; unless the implementers are actually keys? I get the impression that they are simply 'keyed', or have some key associated with them. In which case, IKeyed, IIndexed or something might be better. Then a string Key { get; } becomes more attractive. Perhaps it's just the naming that's the issue here.?
I would call this abuse, because of the problem you hint at right here:
...and you ensure that any calls to the ToString() method on objects which are either cast as the interface IKey or the implementing class will always call the class implementation and not the Object implementation.
Consider the following code:
IKey someKey = ...;
string keyAsString = someKey.ToString();
object someKeyAsObject = (object)someKey;
string keyAsString2 = someKeyAsObject.ToString();
Anybody looking at this code would assume that keyAsString and keyAsString2 are the same. However, these would be calling different methods that may have different behavior. Eek!
Horrendous, if I have to pick just one word... Confused and suspicious would more accurately describe my reaction if I came across this in the wild.
I try to follow one rule above all others when designing API's: Do not surprise the developer.
This would most certainly be a surprise. It precludes the use of the expected output and usage of ToString() without special effort. The fact that there's no indication of the special effort required would be the "surprise" bit. The default implementation of ToString() ends up getting used more often than I would have expected. I would avoid prohibiting or distorting its usage unless I had no other reasonable way to solve an issue.
I don't think this would be "more natural" than a well named method/property that isn't already a member of object.
Just came across this. What about having the interface inherit IFormattable?
http://msdn.microsoft.com/en-us/library/system.iformattable.aspx
I haven't done this myself so I might be wrong, but that seems to enable use of a format parameter for a ToString method for your interface. Note you are still not alterring the parameterless ToString, which I agree with others should not be done in an interface, but instead you make use of ToString(string format, IFormatProvider provider) with a recognizable format input that basically means "give me a description of this object in the context that it implements IWhatever". Obviously each implemented classes will need to code the method, but that is only proper.
So I have a very simple class with one string as property. This string has to have a certain pattern. I'm trying to enforce this using code contracts. The class looks something like this:
class SimpleClass
{
public Property { get; set; }
public SimpleClass(string prop)
{
Contract.Requires(IsValid(prop));
this.Property = prop;
}
[ContractInvariantMethod]
void ObjectInvariant()
{
Contract.Invariant(IsValid(Property));
}
bool IsValid(string arg)
{
// Use regex to check if arg is a valid string
}
}
Very straightforward. However, this throws an unreadable exception and another one saying that 'Member SimpleClass.IsValid has less visibility than the enclosing method SimpleClass.#ctor(System.String)'. Why is this illegal? Should I copy/paste the regex into both methods? That seems to be the opposite of right. Please help me understand!
Another way is avoid 'primitive obsession' and use a class tailored to your purpose, e.g.:
public SimpleClass(Email address)
{
// no need to check, it must be valid :)
}
... and then encapsulate all your validation logic in the Email class. You'll still have the "string format" issues about validation, but I think a better idiom for this is to create a method called Email.TryParse, and fashion it along the lines of int.TryParse.
Just mark IsValid as public and you'll be fine. All "components" of a public surface contract have to be public as well, otherwise there is no way for a caller to check that the contract is satisfied.
#AI-CII I understand that, but that would be a design flaw as well, exposing implementation details to consumers.
A contract on a public method is not an implementation detail. A Contract.Requires says "hey, I require this to be true for me to do some work for you." If "this" isn't visible to the caller, how can the caller verify that the contract is satisfied?
You aren't exposing the implementation details of the method IsValid, you are only exposing what must be satisfied for the callee to do its job.
As Jason already stated, Code Contracts requires the method to be public as you already figured out yourself thanks to the exception message.
I understand however that simply making it public doesn't feel right. Perhaps the regex condition can be encapsulated to a static global function of a helper class?
E.g. If it were to check whether a string is a valid URL.
UrlHelper.IsValidUrl( string url )
This interested me so I started doing some googling. There is a solution! Although I would still prefer the helper class with the static method where possible.
It is called Code Contract Abbreviators. You need to include the sourcefile to your project yourself however.
What I am looking for is a way to call a method after another method has been invoked but before it is entered. Example:
public class Test {
public void Tracer ( ... )
{
}
public int SomeFunction( string str )
{
return 0;
}
public void TestFun()
{
SomeFunction( "" );
}
}
In the example above I would like to have Tracer() called after SomeFunction() has been invoked by TestFun() but before SomeFunction() is entered. I'd also like to get reflection data on SomeFunction().
I found something interesting in everyone's answers. The best answer to the question is to use Castle's DynamicProxy; however, this is not that I'm going to use to solve my problem because it requires adding a library to my project. I have only a few methods that I need to "trace" so I've chosen to go with a modified "core" methodology mixed with the way Dynamic Proxy is implemented. I explain this in my answer to my own question below.
Just as a note I'm going to be looking into AOP and the ContextBoundObject class for some other applications.
You can use a dynamic proxy (Castle's DynamicProxy for example) to intercept the call, run whatever code you wish, and then either invoke your method or not, depending on your needs.
Use a *Core method:
public int SomeFunction(string str)
{
Tracer();
return SomeFunctionCore(str);
}
private int SomeFunctionCore(string str)
{
return 0;
}
A number of the .NET APIs use this (lots do in WPF).
Use delegates!
delegate void SomeFunctionDelegate(string s);
void Start()
{
TraceAndThenCallMethod(SomeFunction, "hoho");
}
void SomeFunction(string str)
{
//Do stuff with str
}
void TraceAndThenCallMethod(SomeFunctionDelegate sfd, string parameter)
{
Trace();
sfd(parameter);
}
You want to look into Aspect Oriented Programming. Here's a page I found for AOP in .NET: http://www.postsharp.org/aop.net/
Aspect Oriented Programming involves separating out "crosscutting concerns" from code. One example of this is logging - logging exists (hopefully) across all of your code. Should these methods all really need to know about logging? Maybe not. AOP is the study of separating these concerns from the code they deal with, and injecting them back in, either at compile-time or run-time. The link I posted contains links to several tools that can be used for both compile-time and run-time AOP.
.NET has a class called ContextBoundObject that you can use to setup message sinks to do call interception as long as you don't mind deriving from a base class this will give you what you are looking for without taking an library dependency.
You would have to use some form of AOP framework like SpringFramework.NET to do that.
If you need to do this on large scale (i.e. for every function in a program) and you don't want to hugely alter the source, you might look into using the .NET Profiling API. Its a little hairy to use since you have to build free-threaded COM objects to do so, but it gives you an enormous amount of control over the execution of the program.
This is the solution I've choosen to solve my problem. Since there is no automatic (attribute like) way to make this work I feel it is the least obtrusive and allows the functionality to be turned on and off by choosing what class get instantiated. Please note that this is not the best answer to my question but it is the better answer for my particular situation.
What's going on is that we're simply deriving a second class that sometimes or always be instantiated in place of its parent. The methods that we want to trace (or otherwise track) are declared virtual and reimplemented in the derived class to perform whatever actions we want to trace and then the function is called in the parent class.
public class TestClass {
public virtual void int SomeFunction( string /*str*/ )
{
return 0;
}
public void TestFun()
{
SomeFunction( "" );
}
}
public class TestClassTracer : TestClass {
public override void int SomeFunction( string str )
{
// do something
return base.SomeFunction( str );
}
}