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How to use the type equivalence feature in .NET?
2019 Community Moderator ElectionHow do I calculate someone's age in C#?Hidden Features of C#?How do I enumerate an enum in C#?How do I get a consistent byte representation of strings in C# without manually specifying an encoding?Difference between decimal, float and double in .NET?Interop type cannot be embeddedWhat is a NullReferenceException, and how do I fix it?Type or namespace name does not existThe type or namespace name does not exist in the namespace 'System.Web.Mvc'Could not find a part of the path … binroslyncsc.exe
I am trying to understand the type equivalence feature of .NET. I created three projects in a solution, two libraries and one console application.
In the libraries I have defined these types:
ClassLibrary1:
namespace ClassLibrary1
[TypeIdentifier("scope1", "identifier1")]
public interface IInterface1
ClassLibrary2:
namespace ClassLibrary2
[TypeIdentifier("scope1", "identifier1")]
public interface IInterface1
I did this based on the documentation here:
https://docs.microsoft.com/en-us/dotnet/framework/interop/type-equivalence-and-embedded-interop-types
And in the console application:
static void Main(string[] args)
ClassLibrary1.IInterface1 variable1 = null;
ClassLibrary2.IInterface1 variable2 = null;
variable1 = variable2;
I am getting these compilation error:
Error CS0234 The type or namespace name 'IInterface1' does not exist in the namespace 'ClassLibrary2' (are you missing an assembly reference?)
Error CS0234 The type or namespace name 'IInterface1' does not exist in the namespace 'ClassLibrary1' (are you missing an assembly reference?)
If remove the TypeIdentifier attribute from the interface definitions, these two errors go away, but of course the compiler wouldn't allow the variable assignments because these are different types.
My question is why do the types seem to disappear if I annotate them with the TypeIdentifier attribute? And how to use type equivalence in .NET?
UPDATE: I tried to reference the libraries as DLLs instead of projects and I get the same result.
UPDATE:
I was able to make type equivalence work in both the .NET framework and .NET Core 3.
Source code can be found here: https://github.com/ymassad/TypeEquivalenceExample
So my current understanding is that the TypeIdentifier attribute is not supposed to be used by developers directly.
When project A references project B, it can specify that it wants to "Embed Interop Types". There are certain conditions for this to work, but the result is that types from B that are used in A are copied inside the Assembly generated when compiling A. These types will be annotated with this attribute by the compiler. It seems that this feature is specifically designed to enable .NET apps to use COM types without the need to deploy an assembly called the "Primary Interop Assembly". This PIA assembly contains all the metadata required to speak with a certain COM based library. If an application/library requires only a few types from this library, it can choose to embed just these types inside itself. Type equivalence is needed here so that different types embedded in different assemblies can be used interchangeably.
I cannot find any documentation explaining why using this feature in the direct way I am describing in this question cannot work. I would appreciate if someone can shed some light on this. Is there a way to make things work in the way described by this question?
c# .net clr
asked Mar 7 at 10:43
Yacoub MassadYacoub Massad
23.8k21944
|
show 3 more comments
I am trying to understand the type equivalence feature of .NET. I created three projects in a solution, two libraries and one console application.
In the libraries I have defined these types:
ClassLibrary1:
namespace ClassLibrary1
[TypeIdentifier("scope1", "identifier1")]
public interface IInterface1
ClassLibrary2:
namespace ClassLibrary2
[TypeIdentifier("scope1", "identifier1")]
public interface IInterface1
I did this based on the documentation here:
https://docs.microsoft.com/en-us/dotnet/framework/interop/type-equivalence-and-embedded-interop-types
And in the console application:
static void Main(string[] args)
ClassLibrary1.IInterface1 variable1 = null;
ClassLibrary2.IInterface1 variable2 = null;
variable1 = variable2;
I am getting these compilation error:
Error CS0234 The type or namespace name 'IInterface1' does not exist in the namespace 'ClassLibrary2' (are you missing an assembly reference?)
Error CS0234 The type or namespace name 'IInterface1' does not exist in the namespace 'ClassLibrary1' (are you missing an assembly reference?)
If remove the TypeIdentifier attribute from the interface definitions, these two errors go away, but of course the compiler wouldn't allow the variable assignments because these are different types.
My question is why do the types seem to disappear if I annotate them with the TypeIdentifier attribute? And how to use type equivalence in .NET?
UPDATE: I tried to reference the libraries as DLLs instead of projects and I get the same result.
UPDATE:
I was able to make type equivalence work in both the .NET framework and .NET Core 3.
Source code can be found here: https://github.com/ymassad/TypeEquivalenceExample
So my current understanding is that the TypeIdentifier attribute is not supposed to be used by developers directly.
When project A references project B, it can specify that it wants to "Embed Interop Types". There are certain conditions for this to work, but the result is that types from B that are used in A are copied inside the Assembly generated when compiling A. These types will be annotated with this attribute by the compiler. It seems that this feature is specifically designed to enable .NET apps to use COM types without the need to deploy an assembly called the "Primary Interop Assembly". This PIA assembly contains all the metadata required to speak with a certain COM based library. If an application/library requires only a few types from this library, it can choose to embed just these types inside itself. Type equivalence is needed here so that different types embedded in different assemblies can be used interchangeably.
I cannot find any documentation explaining why using this feature in the direct way I am describing in this question cannot work. I would appreciate if someone can shed some light on this. Is there a way to make things work in the way described by this question?
c# .net clr
asked Mar 7 at 10:43
Yacoub MassadYacoub Massad
23.8k21944
1
I'm curious why you are even trying to do this? This was useful in the days of COM but I've not seen it used for a very long time.
– DavidG
Mar 7 at 10:52
@DavidG, this is a potential solution for a problem that I am trying to solve. The problem is to big to present here. Based on the fact that COM interfaces embedded in different assemblies can be used interchangeably, I wondered if I can use this feature outside of COM.
– Yacoub Massad
Mar 7 at 12:09
Well without your specific use case it's hard to suggest alternatives. The usual option would be to have classes in their own DLL and share that around, that usually makes all this go away. Or use a mapping tool like AutoMapper. Of course this might not be useful in your situation.
– DavidG
Mar 7 at 12:11
@DavidG, that wouldn't be useful in my situation. Since this is a documented feature, I expect this to work. I wonder if the feature is intentionally disabled for non-COM scenarios.
– Yacoub Massad
Mar 7 at 12:13
@YacoubMassad: It's a documented feature in terms of COM types. The documentation refers to COM types all over the place, e.g. "Equivalence of COM types is supported for interfaces, structures, enumerations, and delegates." I don't think it's reasonable to expect it to work for non-COM types, given the heavy emphasis of COM in all the documentation. I would strongly advise you to look for a different solution to whatever your original problem is. (We can't give advice on how to solve the problem, as all we know is how you're already trying to solve it in a way that doesn't work.)
– Jon Skeet
Mar 9 at 9:58
|
show 3 more comments
I am trying to understand the type equivalence feature of .NET. I created three projects in a solution, two libraries and one console application.
In the libraries I have defined these types:
ClassLibrary1:
namespace ClassLibrary1
[TypeIdentifier("scope1", "identifier1")]
public interface IInterface1
ClassLibrary2:
namespace ClassLibrary2
[TypeIdentifier("scope1", "identifier1")]
public interface IInterface1
I did this based on the documentation here:
https://docs.microsoft.com/en-us/dotnet/framework/interop/type-equivalence-and-embedded-interop-types
And in the console application:
static void Main(string[] args)
ClassLibrary1.IInterface1 variable1 = null;
ClassLibrary2.IInterface1 variable2 = null;
variable1 = variable2;
I am getting these compilation error:
Error CS0234 The type or namespace name 'IInterface1' does not exist in the namespace 'ClassLibrary2' (are you missing an assembly reference?)
Error CS0234 The type or namespace name 'IInterface1' does not exist in the namespace 'ClassLibrary1' (are you missing an assembly reference?)
If remove the TypeIdentifier attribute from the interface definitions, these two errors go away, but of course the compiler wouldn't allow the variable assignments because these are different types.
My question is why do the types seem to disappear if I annotate them with the TypeIdentifier attribute? And how to use type equivalence in .NET?
UPDATE: I tried to reference the libraries as DLLs instead of projects and I get the same result.
UPDATE:
I was able to make type equivalence work in both the .NET framework and .NET Core 3.
Source code can be found here: https://github.com/ymassad/TypeEquivalenceExample
So my current understanding is that the TypeIdentifier attribute is not supposed to be used by developers directly.
When project A references project B, it can specify that it wants to "Embed Interop Types". There are certain conditions for this to work, but the result is that types from B that are used in A are copied inside the Assembly generated when compiling A. These types will be annotated with this attribute by the compiler. It seems that this feature is specifically designed to enable .NET apps to use COM types without the need to deploy an assembly called the "Primary Interop Assembly". This PIA assembly contains all the metadata required to speak with a certain COM based library. If an application/library requires only a few types from this library, it can choose to embed just these types inside itself. Type equivalence is needed here so that different types embedded in different assemblies can be used interchangeably.
I cannot find any documentation explaining why using this feature in the direct way I am describing in this question cannot work. I would appreciate if someone can shed some light on this. Is there a way to make things work in the way described by this question?
c# .net clr
asked Mar 7 at 10:43
Yacoub MassadYacoub Massad
23.8k21944
I am trying to understand the type equivalence feature of .NET. I created three projects in a solution, two libraries and one console application.
In the libraries I have defined these types:
ClassLibrary1:
namespace ClassLibrary1
[TypeIdentifier("scope1", "identifier1")]
public interface IInterface1
ClassLibrary2:
namespace ClassLibrary2
[TypeIdentifier("scope1", "identifier1")]
public interface IInterface1
I did this based on the documentation here:
https://docs.microsoft.com/en-us/dotnet/framework/interop/type-equivalence-and-embedded-interop-types
And in the console application:
static void Main(string[] args)
ClassLibrary1.IInterface1 variable1 = null;
ClassLibrary2.IInterface1 variable2 = null;
variable1 = variable2;
I am getting these compilation error:
Error CS0234 The type or namespace name 'IInterface1' does not exist in the namespace 'ClassLibrary2' (are you missing an assembly reference?)
Error CS0234 The type or namespace name 'IInterface1' does not exist in the namespace 'ClassLibrary1' (are you missing an assembly reference?)
If remove the TypeIdentifier attribute from the interface definitions, these two errors go away, but of course the compiler wouldn't allow the variable assignments because these are different types.
My question is why do the types seem to disappear if I annotate them with the TypeIdentifier attribute? And how to use type equivalence in .NET?
UPDATE: I tried to reference the libraries as DLLs instead of projects and I get the same result.
UPDATE:
I was able to make type equivalence work in both the .NET framework and .NET Core 3.
Source code can be found here: https://github.com/ymassad/TypeEquivalenceExample
So my current understanding is that the TypeIdentifier attribute is not supposed to be used by developers directly.
When project A references project B, it can specify that it wants to "Embed Interop Types". There are certain conditions for this to work, but the result is that types from B that are used in A are copied inside the Assembly generated when compiling A. These types will be annotated with this attribute by the compiler. It seems that this feature is specifically designed to enable .NET apps to use COM types without the need to deploy an assembly called the "Primary Interop Assembly". This PIA assembly contains all the metadata required to speak with a certain COM based library. If an application/library requires only a few types from this library, it can choose to embed just these types inside itself. Type equivalence is needed here so that different types embedded in different assemblies can be used interchangeably.
I cannot find any documentation explaining why using this feature in the direct way I am describing in this question cannot work. I would appreciate if someone can shed some light on this. Is there a way to make things work in the way described by this question?
c# .net clr
c# .net clr
asked Mar 7 at 10:43
Yacoub MassadYacoub Massad
23.8k21944
asked Mar 7 at 10:43
Yacoub MassadYacoub Massad
23.8k21944
edited Mar 9 at 9:39
Yacoub Massad
asked Mar 7 at 10:43
Yacoub MassadYacoub Massad
23.8k21944
asked Mar 7 at 10:43
Yacoub MassadYacoub Massad
23.8k21944
asked Mar 7 at 10:43
Yacoub MassadYacoub Massad
23.8k21944
23.8k21944
1
I'm curious why you are even trying to do this? This was useful in the days of COM but I've not seen it used for a very long time.
– DavidG
Mar 7 at 10:52
@DavidG, this is a potential solution for a problem that I am trying to solve. The problem is to big to present here. Based on the fact that COM interfaces embedded in different assemblies can be used interchangeably, I wondered if I can use this feature outside of COM.
– Yacoub Massad
Mar 7 at 12:09
Well without your specific use case it's hard to suggest alternatives. The usual option would be to have classes in their own DLL and share that around, that usually makes all this go away. Or use a mapping tool like AutoMapper. Of course this might not be useful in your situation.
– DavidG
Mar 7 at 12:11
@DavidG, that wouldn't be useful in my situation. Since this is a documented feature, I expect this to work. I wonder if the feature is intentionally disabled for non-COM scenarios.
– Yacoub Massad
Mar 7 at 12:13
@YacoubMassad: It's a documented feature in terms of COM types. The documentation refers to COM types all over the place, e.g. "Equivalence of COM types is supported for interfaces, structures, enumerations, and delegates." I don't think it's reasonable to expect it to work for non-COM types, given the heavy emphasis of COM in all the documentation. I would strongly advise you to look for a different solution to whatever your original problem is. (We can't give advice on how to solve the problem, as all we know is how you're already trying to solve it in a way that doesn't work.)
– Jon Skeet
Mar 9 at 9:58
|
show 3 more comments
1
I'm curious why you are even trying to do this? This was useful in the days of COM but I've not seen it used for a very long time.
– DavidG
Mar 7 at 10:52
@DavidG, this is a potential solution for a problem that I am trying to solve. The problem is to big to present here. Based on the fact that COM interfaces embedded in different assemblies can be used interchangeably, I wondered if I can use this feature outside of COM.
– Yacoub Massad
Mar 7 at 12:09
Well without your specific use case it's hard to suggest alternatives. The usual option would be to have classes in their own DLL and share that around, that usually makes all this go away. Or use a mapping tool like AutoMapper. Of course this might not be useful in your situation.
– DavidG
Mar 7 at 12:11
@DavidG, that wouldn't be useful in my situation. Since this is a documented feature, I expect this to work. I wonder if the feature is intentionally disabled for non-COM scenarios.
– Yacoub Massad
Mar 7 at 12:13
@YacoubMassad: It's a documented feature in terms of COM types. The documentation refers to COM types all over the place, e.g. "Equivalence of COM types is supported for interfaces, structures, enumerations, and delegates." I don't think it's reasonable to expect it to work for non-COM types, given the heavy emphasis of COM in all the documentation. I would strongly advise you to look for a different solution to whatever your original problem is. (We can't give advice on how to solve the problem, as all we know is how you're already trying to solve it in a way that doesn't work.)
– Jon Skeet
Mar 9 at 9:58
1
1
I'm curious why you are even trying to do this? This was useful in the days of COM but I've not seen it used for a very long time.
– DavidG
Mar 7 at 10:52
I'm curious why you are even trying to do this? This was useful in the days of COM but I've not seen it used for a very long time.
– DavidG
Mar 7 at 10:52
@DavidG, this is a potential solution for a problem that I am trying to solve. The problem is to big to present here. Based on the fact that COM interfaces embedded in different assemblies can be used interchangeably, I wondered if I can use this feature outside of COM.
– Yacoub Massad
Mar 7 at 12:09
@DavidG, this is a potential solution for a problem that I am trying to solve. The problem is to big to present here. Based on the fact that COM interfaces embedded in different assemblies can be used interchangeably, I wondered if I can use this feature outside of COM.
– Yacoub Massad
Mar 7 at 12:09
Well without your specific use case it's hard to suggest alternatives. The usual option would be to have classes in their own DLL and share that around, that usually makes all this go away. Or use a mapping tool like AutoMapper. Of course this might not be useful in your situation.
– DavidG
Mar 7 at 12:11
Well without your specific use case it's hard to suggest alternatives. The usual option would be to have classes in their own DLL and share that around, that usually makes all this go away. Or use a mapping tool like AutoMapper. Of course this might not be useful in your situation.
– DavidG
Mar 7 at 12:11
@DavidG, that wouldn't be useful in my situation. Since this is a documented feature, I expect this to work. I wonder if the feature is intentionally disabled for non-COM scenarios.
– Yacoub Massad
Mar 7 at 12:13
@DavidG, that wouldn't be useful in my situation. Since this is a documented feature, I expect this to work. I wonder if the feature is intentionally disabled for non-COM scenarios.
– Yacoub Massad
Mar 7 at 12:13
@YacoubMassad: It's a documented feature in terms of COM types. The documentation refers to COM types all over the place, e.g. "Equivalence of COM types is supported for interfaces, structures, enumerations, and delegates." I don't think it's reasonable to expect it to work for non-COM types, given the heavy emphasis of COM in all the documentation. I would strongly advise you to look for a different solution to whatever your original problem is. (We can't give advice on how to solve the problem, as all we know is how you're already trying to solve it in a way that doesn't work.)
– Jon Skeet
Mar 9 at 9:58
@YacoubMassad: It's a documented feature in terms of COM types. The documentation refers to COM types all over the place, e.g. "Equivalence of COM types is supported for interfaces, structures, enumerations, and delegates." I don't think it's reasonable to expect it to work for non-COM types, given the heavy emphasis of COM in all the documentation. I would strongly advise you to look for a different solution to whatever your original problem is. (We can't give advice on how to solve the problem, as all we know is how you're already trying to solve it in a way that doesn't work.)
– Jon Skeet
Mar 9 at 9:58
|
show 3 more comments
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1
I'm curious why you are even trying to do this? This was useful in the days of COM but I've not seen it used for a very long time.
– DavidG
Mar 7 at 10:52
@DavidG, this is a potential solution for a problem that I am trying to solve. The problem is to big to present here. Based on the fact that COM interfaces embedded in different assemblies can be used interchangeably, I wondered if I can use this feature outside of COM.
– Yacoub Massad
Mar 7 at 12:09
Well without your specific use case it's hard to suggest alternatives. The usual option would be to have classes in their own DLL and share that around, that usually makes all this go away. Or use a mapping tool like AutoMapper. Of course this might not be useful in your situation.
– DavidG
Mar 7 at 12:11
@DavidG, that wouldn't be useful in my situation. Since this is a documented feature, I expect this to work. I wonder if the feature is intentionally disabled for non-COM scenarios.
– Yacoub Massad
Mar 7 at 12:13
@YacoubMassad: It's a documented feature in terms of COM types. The documentation refers to COM types all over the place, e.g. "Equivalence of COM types is supported for interfaces, structures, enumerations, and delegates." I don't think it's reasonable to expect it to work for non-COM types, given the heavy emphasis of COM in all the documentation. I would strongly advise you to look for a different solution to whatever your original problem is. (We can't give advice on how to solve the problem, as all we know is how you're already trying to solve it in a way that doesn't work.)
– Jon Skeet
Mar 9 at 9:58