I am trying to get the name of a method on a generic interface. I would expect this to work as the type part would be a valid typeof:
//This does not compile
nameof(IGenericInterface<>.Method)
//This would compile
typeof(IGenericInterface<>)
I think this should be valid c#-6.0 or am I missing something or is there a better way to do this. I don't want to use a string for the Method name as if the method is renamed code would break without any build-time errors.
This is expected. According to the documentation, your expression is disallowed, because it refers to an unbound generic type:
Because the argument needs to be an expression syntactically, there are many things disallowed that are not useful to list. The following are worth mentioning that produce errors: predefined types (for example, int or void), nullable types (Point?), array types (Customer[,]), pointer types (Buffer*), qualified alias (A::B), and unbound generic types (Dictionary<,>), preprocessing symbols (DEBUG), and labels (loop:).
You can work around this limitation by supplying a generic parameter:
nameof(IGenericInterface<object>.Method)
Note: I think Microsoft should tweak nameof feature to allow references to methods of unbound generic types.
Just use a sample type in order to compile.
string name = nameof(IGenericInterface<int>.Method) // will be Method
The solutions presented with "sample types" will work, but sooner or later you will need to get the nameof a generic type which has type constraints, so nameof(MyGenericType<object>) won't work, because object does not abide by the constraints.
If you find yourself in this situation, it might seem that you have to declare a dummy little class real quick which abides by the constraints so that you can get its nameof, but having to do something as hacky as that is a clear indication that you are down the wrong rabbit hole.
Here is a better solution:
typeof(MyGenericType<>).Name
Interestingly enough, C# allows us to use <> in typeof but not in nameof. Go figure.
Related
When I use automapper, I purposely don't map a number of properties that are identical. That's one of the main reasons for me to use automapper. Outside of that, I can build a projection or class converter myself with about the same amount of code and less reflection (i.e., more performant).
The only issue I have is that we occasionally have some type mismatches. Is it possible to use automapper's configuration validation to confirm that the types are interchangeable?
I know that for some types, like string to int, that can't be validated 100% because someone could use a string that isn't convertible to an integer. But some types like timespan to datetime are not convertible without an explicit map. I would like to call those out. The existing AssertConfigurationIsValid() method fails to satisfy my needs because of the strict combination of explicit mapping/ignoring needed for it to only ever complain about type mismatches instead.
This is not supported by the library. One possible solution is to write our own validation process that only checks the source and destination type with some variation of casts and try/catching Convert.ChangeType().
I have the following class
public abstract class Result<TResult, TData> where TResult : Result<TResult, TData>
{
public virtual TData Data { get; private set; }
}
How can I use nameof on the Data property?
It tried some options but got compilation errors
nameof(Result<object, object>.Data)
Error CS0311
The type 'object' cannot be used as type parameter 'TResult' in the generic type or method
'Result<TResult, TData>'. There is no implicit reference conversion from 'object' to
'Result<object, object>'
UPDATE
To better specify:
I did not write the class in the first snippet, but I have to use it as it is.
I need to use reflection to get a PropertyInfo instance for the Data property. I can do it by calling GetProperty("Data"), but I prefer to avoid strings in case the name property is renamed with the Visual Studio Refactoring (for example from Data to Content).
I cannot use nameof(Data) and I am in a different context that doesn't know about the Data property in that class.
As such, I would call GetProperty(nameof({whatever}.Data)). Of course, if not possible I would use the string. But if there is a way, I would like to know it.
Unfortunately, the nameof operator does not work with unbound generic types. E.g. you'd like to be able to write nameof(Result<,>.Data), just like you can today write something like typeof(Result<,>). So you would need to specify type parameters when trying to get the nameof(Result<TResult, TData>.Data) value.
Which you've tried, but you provided object as the type parameter for both parameters, even though your generic type constrains TResult as being derived from Result<TResult, TData>. The type object doesn't meet the constraint, so that can't possibly work. Hence the compiler error.
Obviously, if you can provide any type that does meet the constraint, that would solve the compiler error and allow you to use the nameof operator. There's not enough information in your question to know whether that's an option in your specific scenario.
I agree with this comment that you would probably be better off asking a different question, one which takes a step back and explains how you arrived at feeling you needed this syntax in the first place. It's not clear what the broader goal you're trying to accomplish is, where you don't have known type parameters to use for this expression. Typically, code outside of the generic type that wants to make use of the generic type, would actually know the type parameters it intends to use with the generic type.
Note that in the context of the generic type itself, you can refer to the property without knowing the exact type parameters, since the property identifier does not need qualification. E.g. nameof(Data) would work, for any code that's actually in the generic class Result<TResult, TData>. Whether that helps in your specific scenario is unclear from the information provided so far.
I am trying to get the name of a method on a generic interface. I would expect this to work as the type part would be a valid typeof:
//This does not compile
nameof(IGenericInterface<>.Method)
//This would compile
typeof(IGenericInterface<>)
I think this should be valid c#-6.0 or am I missing something or is there a better way to do this. I don't want to use a string for the Method name as if the method is renamed code would break without any build-time errors.
This is expected. According to the documentation, your expression is disallowed, because it refers to an unbound generic type:
Because the argument needs to be an expression syntactically, there are many things disallowed that are not useful to list. The following are worth mentioning that produce errors: predefined types (for example, int or void), nullable types (Point?), array types (Customer[,]), pointer types (Buffer*), qualified alias (A::B), and unbound generic types (Dictionary<,>), preprocessing symbols (DEBUG), and labels (loop:).
You can work around this limitation by supplying a generic parameter:
nameof(IGenericInterface<object>.Method)
Note: I think Microsoft should tweak nameof feature to allow references to methods of unbound generic types.
Just use a sample type in order to compile.
string name = nameof(IGenericInterface<int>.Method) // will be Method
The solutions presented with "sample types" will work, but sooner or later you will need to get the nameof a generic type which has type constraints, so nameof(MyGenericType<object>) won't work, because object does not abide by the constraints.
If you find yourself in this situation, it might seem that you have to declare a dummy little class real quick which abides by the constraints so that you can get its nameof, but having to do something as hacky as that is a clear indication that you are down the wrong rabbit hole.
Here is a better solution:
typeof(MyGenericType<>).Name
Interestingly enough, C# allows us to use <> in typeof but not in nameof. Go figure.
I need to loop over a List<dynamic> objects.
The list's objects all have values, but for some reason, I am not able to access any of the dynamic object fields. Below is a screenshot of my debug window:
There you can see the object contains fields (such Alias, Id, Name, etc).
I tried both casting it to a IDictionary<string, object> and ExpandoObject, to no avail. I did not face such a thing before: failing to access existing fields in a dynamic object when they exist.
What is wrong here?
The code is throwing a Microsoft.CSharp.RuntimeBinder.RuntimeBinderException with a message stating {"'object' does not contain a definition for 'Name'"}.
The list was created adding anonymously-typed objects, like this:
return new List<dynamic>(fields.Select(field => new
{
Id = field.Id,
Alias = field.Alias,
Name = field.Name,
Type = field.Type,
Value = field.Value,
SortOrder = field.SortOrder
}));
where fields is an ICollection<Field>, a strongly-typed collection.
The telling part is the exception:
{"'object' does not contain a definition for 'Name'"}.
This indicates that the runtime binder was not actually capable of accessing the type you're passing in dynamic (since dynamic does actually enforce visibility rules).
The most likely cause of this is that you're creating the anonymous type in a different assembly from the one where you're subsequently reading it - since anonymous types are declared internal, the consuming assembly cannot access it, causing the error message above.
Contrast with the usual case of runtime binder exceptions:
'<>f__AnonymousType0< string >' does not contain a definition for 'Name'
EDIT:
A possible solution to the problem is to use the InternalsVisibleToAttribute on the assembly containing the anonymous type. However, this is code smell - just like any other use of InternalsVisibleToAttribute or internal itself.
A better way would be to make sure you don't actually pass anonymous types over assembly boundaries - after all, they shouldn't even be used outside of the method they originated from; the fact that they are is basically an implementation detail of .NET - they didn't have another way to do the same thing. This could change in future versions, making the InternalsVisibleToAttribute solution doubly unreliable.
The way your code is using dynamic suggests that your team has flawed assumptions about how dynamic works and how it's supposed to be used. Note how the actual runtime type of List<dynamic> is actually List<object>. The same goes for arguments of type dynamic (which are again just object, albeit marked with DynamicAttribute). And in fact, that really is what dynamic is - it's a way to handle runtime dynamic dispatch - it's not a property of the type or anything, it's just the way you actually invoke whatever you're trying to invoke. For C#, dynamic allows you to skip most of the compiler checks when working with those dynamic types, and it generates some code to handle the dispatch for you automatically, but all of that only happens inside the method where you actually use the dynamic keyword - if you used List<object>, the end result would be exactly the same.
In your code, there's no reason not to use simple static types. Dynamic typing doesn't really give you any benefits, apart from the effort to code the types themselves. If your co-workers don't like that, well, they should present a better solution - the problem is quite obvious, and it's something you need to deal with.
Much worse, it explicitly hides all context, all the type information. That's not something you want in an API, internal or not! If you want to hide the concrete types being used, why not - but you should still expose an interface instead. I suspect this is the reason why anonymous types can't implement interfaces - it would encourage you to go entirely the wrong way.
void LoadParameters<T, TValue>(TValue strategy)
where T : Parameters
Saw a code like this. Will the program still work correctly without the where statement?
If it compiles without the where statement, it will work correctly. However, chances are the coder did not simply put it there without reason. If you remove it, it will likely not compile and hence not work.
That where clause is called a "generic type constraint". Usually T can be any type and you must write your generic code with that in mind. By constraining T to be, inherit or implement a specific type, you gain the ability to refer to the members of that type in your generic code, because the compiler is assured that any object used will be that type. You can also use class, struct or new as generic type constraints, which enforce T being a reference type, a value type or having a parameterless constructor respectively.