Skip to main content

where enum does not work !!!

I was writing a generic method with enum as the Constraint, and the compiler spat a few errors that did not directly convey me that enums cannot used as generic constraints. And I learnt the following from my investigation:-

This is an excerpt from the C# Language Specification. Enums are value types and there is no way that you can specify the System.ValueType as a constraint, as per the specification. But if you wish to specify a non-reference type as a [primary] constraint, struct can be used.

private void Method where T : struct

That does not guarantee that our generic method will not accept other value types, besides enum, for which we do not support our functionality.

During the course of investigation, I was extremely surprised to know that the numeric types like int, float etc in C# are struct. It is not far from the fact that they are value types, but it was interesting to know that they are declared as


public struct Int32 : IComparable, IFormattable, IConvertible, IComparable, IEquatable

Similar thing for other numeric types. Whereas an enum [System.Enum], though a value type, is declared as an abstract class that derives from System.ValueTypes unlike the int or float. The end result is that enums are value types but i wonder the way they are declared.

Anyway, the question still remains unresolved - why enums cannot be used as constraints, andjust the specification saying that enums cannot be used as constraints is unsatisfactory.

I am not sure if there is any other way to resolve my situation.
Question open to cyber space !!!

P.S.
Refer section 25.7 through for the specification on Generic Type Constraints.

Post a Comment

Popular posts from this blog

Passing CComPtr By Value !!!

This is about a killer bug identified by our chief software engineer in our software. What was devised for ease of use and write smart code ended up in this killer defect due to improper perception. Ok, let us go!CComPtr is a template class in ATL designed to wrap the discrete functionality of COM object management - AddRef and Release. Technically it is a smart pointer for a COM object.void SomeMethod() { CComPtr siPtr; HRESULT hr = siPtr.CoCreateInstance(CLSID_SomeComponent); siPtr->MethodOne(20, L"Hello"); }Without CComPtr, the code wouldn't be as elegant as above. The code would be spilled with AddRef and Release. Besides, writing code to Release after use under any circumstance is either hard or ugly. CComPtr automatically takes care of releasing in its destructor just like std::auto_ptr. As a C++ programmer, we must be able to appreciate the inevitability of the destructor and its immense use in writing smart code. However there is a difference between …

out, ref and InvokeMember !!!

When I was working on the .NET reflection extravaganza thing that I explained in my previous column, i learnt one another interesting thing, that is about the Type.InvokeMember. How will pass out or ref parameters for the method invoked using Type.InvokeMember ? If you are going to invoke a method with the prototypeint DoSomething(string someString, int someInt);then you would use InvokeMember like this:-object obj = someType.InvokeMember("DoSomething",
BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance,
null,
this,
new object[] {"Largest Integer", 1});or use some variables in the new object[] {...}. But what do you with the args if DoSomething takes out or ref parameters ?int DoSomething(out string someString, ref int someInt);Something like this will not work string someText = string.Empty;
int someInt = 0;
object obj = someType.InvokeMember("DoSomething",
BindingFlags.Public | BindingFlags.NonPublic …

Offering __FILE__ and __LINE__ for C# !!!

THIS POST USES SYNTAXHIGHLIGHTER AND HAS ISSUES RENDERING CODE ONLY IN CHROME
Not the same way but we could say better.
Visual Studio 2012, another power packed release of Visual Studio, among a lot of other powerful fancy language features, offers the ability to deduce the method caller details at compile time.
C++ offered the compiler defined macros __FILE__ and __LINE__ (and __DATE__ and __TIME__), which are primarily intended for diagnostic purposes in a program, whereby the caller information is captured and logged. For instance, using __LINE__ would be replaced with the exact line number in the file where this macro has been used. That sometimes beats the purpose and doesn't gives us what we actually expect. Let's see.

For instance, suppose you wish to write a verbose Log method with an idea to print rich diagnostic details, it would look something like this.
void LogException(const std::string& logText, const std::string& fileName, …