This question already has answers here:
Can you get merged attributes for a class in C#?
(2 answers)
Closed 9 years ago.
I have a certain collection of built-in attributes (like System.Runtime.Serialization.SerializableAttribute) that I want to apply to a certain collection of classes
Is it possible to unite those attributes into one? I don't want to apply all of them to all of my classes explicitly (the attibute collection might change during the development process)
What I want is one attribute, e.g.
public class MyClassAttribute: System.Attribute { ... }
which I could apply easily to my classes
[MyClass]
public class SampleClass { ... }
and that would cause SampleClass to have Serializable attribute and others. Thanks
No, it is not, basically. Actually, [Serializable] is particularly note-worthy because that has different treatment in the compiler - it is not written as an attribute, but as a raw flag (the runtime simply lies if you ask "does it have the [Serializable] attribute" - it checks the flag against the type, and returns what you expect to see, even though that isn't the truth).
I don't think it's possible out of the box, but you could use Mono.Cecil to modify the types in your assembly in a post-build step, removing your collection-attribute and adding the others.
Interesting question. I think a lot of the built-in attributes are sealed so this might not be possible.
Related
I find myself writing a lot of this kind of stuff:
[SameAttribute]
ClassA fieldA;
[SameAttribute]
ClassB fieldB;
[SameAttribute]
ClassC fieldC;
...
Is there a syntax in C# that would allow me to mark several fields with the same attribute at once? May be there are coding conventions about this situation that would make this code less verbose and more readable?
Edit: Just to clarify, I don't want every field of the class to have this attribute, there's just a lot of them.
No. You will have to apply the [SameAttribute] to each field individually.
If you want SomeAttribute to apply to all fields in a class, it might be possible to apply the attribute to the entire class. However, even if SomeAttribute is allowed to target classes, its exact behavior when doing so is dependent on the implementation of SomeAttribute. Otherwise no, you have to apply the attribute to each field individually.
In addition to the other answers above, PostSharp, which allows "aspect-oriented programming" lets you define attributes that will apply to each member in a class. You can use it to make a custom attribute that would apply your desired attribute to all of the members.
There is nothing out of the box, that I know of, but you could use a Visual Studio add-in like ReSharper to create a live template to automatically add the Attribute you wish to use when you use a certain template
http://www.jetbrains.com/resharper/features/code_templates.html
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Interface defining a constructor signature?
I have a mixed hierarchy of classes and interfaces.
For using serialisation I need a default constructor present in
each class. I would really aprreciate if the compiler could tell
me that a default constructor is missing somewhere in the hierarchy.
(seeing the problem at compile time, not in the later tests)
What I would like to have could be some markup or attribute,
but I could not find anything.
Something like:
[ForceDefaultConstructor]
interface IVeryQuickSerializable
{
Serialize();
Deserialize();
}
would be great!
But anything like that is very appreciated.
There is a limitation: I cannot change the Serialisation.
Making it generic would solve the problem, but I do not have
the source. Writing a wrapper might do the job, but it will
have a loophole for objects deriving from the toplevel Serialisation
interface (which may not be altered).
You can't do that in an interface or attribute.
Two thoughts:
integration test: use reflection to find all relevant classes, and check them in a test
expose your serialization code in a generic API that uses the T : new() clause, i.e.
void Serialize<T>(T obj, ...) where T : IVeryQuickSerializable, new()
There most probably are better solutions, but you could write an application that uses reflection to inspect the assembly during the post-build event.
This question already has answers here:
Closed 12 years ago.
Possible Duplicates:
Should I use public properties and private fields or public fields for data?
Property(with no extra processing) vs public field
What is the point in having a property inside a class that simply get and sets a member variable?
What practical difference would be there to just making the variable public?
I think similar questions have been answered on many occasions, but basically it gives you the option of adding error checking/etc validation to your property without changing the public interface.
There's also some good information here, the following quote probably answers your question best:
A property communicates the idea of "I will make a value available to you, or accept a value from you." It's not an implementation concept, it's an interface concept. A field, on the other hand, communicates the implementation - it says "this type represents a value in this very specific way". There's no encapsulation, it's the bare storage format. This is part of the reason fields aren't part of interfaces - they don't belong there, as they talk about how something is achieved rather than what is achieved.
Ease of maintenance... you can log assignments, add validation, etc., without breaking existing callers.
You can't databind to public variables. Only public properties.
If you ever want to change the way the method is accessed, just changing the property is much easier than going through all of your code to find it. Also, you could make the property virtual, change the underlying data type easily, or use a Settings variable so that it's saved and recalled automatically. I had a similar question myself.
Properties allow future expansion in accessors and getters (validation, eventing, etc).
You can also make a property virtual, whereas a field cannot be.
The IL for calling fields is different to that of properties, so if you change a field to a property later on, existing compiled calling code will break.
The point is that caller of your class do not know what field the property gets/sets, whether it's calculated, fetched from somewhere, or whether messing with it causes and update/change to the state of you class instance. With a simple field call none of these are an option.
Is it possible to have something like AttributeUsage to restrict the use of an attribute to a specific class (not just AttributeTargets.Class - that would be any class)?
One way to accomplish this, if you have access to the specific class, is detailed by Marc Gravel here: http://marcgravell.blogspot.com/2009/06/restricting-attribute-usage.html. Basically you implement the attribute as a protected class of the specific type. Then it can only be used by that type.
No. There is nothing in the framework that would do this.
However, the code that uses the attribute in question could always check to make sure that the class's type is the specific class (or one of its subclasses).
Attributes, by themselves, do nothing - so this should have the same effect.
Make all data in the Attribute accessible only by a public static method which takes the class you want in question and checks to see if it has the given attribute.
This question already has answers here:
C#3.0 Automatic properties, why not access the field directly?
(9 answers)
Closed 7 years ago.
Whats the benefit of:
public string User {get; set;}
over
public string User;
Since you can't access the private member in the first case, how is it any different that just making your property public?
The second example is making the field public, not a property (your question). This provides a simple way of making simple properties. Properties should be your default, not public fields; the list of reasons is endless, but starts with:
encapsulation
ability to add notification
encapsulation
ability to do validation
encapsulation
data binding
encapsulation
security checking
oh - and did I mention encapsulation?
Changing from a field to a property after-the-fact is a breaking change - especially if you use a lot of "ref" code or mutable structs (yeuch).
There can be a number of things that you must do when User value changes. Things that you don't know in advance or are not present at the time you design your classes.
For example one day you realize that user value should be at least 5 characters long. If you have and property it simple to implement. If you have a public field you must change that to property and recompile all dependent code.
In essence I think it pays to explicitly separate public/API part of the our types and the private implementation details.
Did someone mentioned encapsulation ? ;)