C# 2.0: Generics, default(T) and compare to null weirdness

re: C# 2.0: Generics, default(T) and compare to null weirdness

Ari — Sun, 16 Oct 2011 16:34:13 GMT

for those who might stumble upon this through search, this might help:

here is a solution: www.geekality.net/.../generics-and-checking-for-null

re: C# 2.0: Generics, default(T) and compare to null weirdness

hagen — Mon, 03 Jan 2011 09:46:20 GMT

to avoid comparing to "null", you might use EqualityComparer<T>.Default.Equals(T x, default(T))

re: C# 2.0: Generics, default(T) and compare to null weirdness

Dan — Tue, 22 Dec 2009 22:29:43 GMT

If a Generic Type T is implementing an interface, it would therefore assume it was a reference type, and thus nullable? isn't this correct.

i.e.

public T x<T>() where T : IMyInterface

{

return null;

}

re: C# 2.0: Generics, default(T) and compare to null weirdness

GuyBehindtheGuy — Wed, 04 Feb 2009 21:12:32 GMT

Thanks for the info! I just ran into this exact problem.

re: C# 2.0: Generics, default(T) and compare to null weirdness

Jonathan Delorme — Wed, 12 Nov 2008 19:39:58 GMT

// The clean way ;)

public static bool IsDefaultValue(T res)

{

return Object.Equals(res, null);

}

re: C# 2.0: Generics, default(T) and compare to null weirdness

Kc Joe — Wed, 21 May 2008 00:25:52 GMT

Oops ... Fixed:

public static bool IsDefaultValue(T res)

{

//Compiler Error

//return (default(T) == res);

var obj = default(T) as object;

if (obj == null) //Is Not Value Type

return (res == null);

if (obj.GetType().IsValueType)

{

if (res == null) //res Is Not A Value Type

return false;

return res.Equals(obj);

}

Debug.Fail("Should Not Reach Here!");

return false;

}

Still Ugly!

re: C# 2.0: Generics, default(T) and compare to null weirdness

Kc Joe — Wed, 21 May 2008 00:19:53 GMT

So If You'd Like To Check Inside A Generic Class If A Variable Eqauls To Default You Should Do:

public bool IsDefault(TInterpretationResult res)

{

//Compiler Error

//return (default(T) == res);

var obj = default(T) as object;

if (obj == null) //Is Not Value Type

return (res == null);

if (obj.GetType().IsValueType)

{

return (ValueType)obj == (ValueType)obj;

}

Debug.Fail("Should Not Reach Here!");

return false;

}

Seems Kinda Ugly, It's Strange That MS Didn't Handle It In A More Elegent Way

re: C# 2.0: Generics, default(T) and compare to null weirdness

jokiz — Thu, 06 Dec 2007 08:54:44 GMT

"The int gets converted to a nullable type" - nope, i checked the IL and it's not, still int32

re: C# 2.0: Generics, default(T) and compare to null weirdness

Sunny — Mon, 09 Jul 2007 19:08:17 GMT

I want to do something like:

class myObject{

public T Fetch<T>(ICriteria oCriteria){

T fetchResult = default(T);

if(T == something){

fetchResult = doSomething();

}

private something doSomething(){

return new something();

}

which gives me a compile time error at fetchResult = doSomething();

Any help?

Regards,

Sunny

re: C# 2.0: Generics, default(T) and compare to null weirdness

Jochen — Thu, 29 Mar 2007 17:46:15 GMT

default(T).Equals(obj);

DOES NOT WORK if T is a reference type since you cannot call .Equals on null...