Nullable types in .NET

Question

 protected static SqlParameter CreateParameter(string name, object value, bool skipEmpty, bool isOutput =false)
 {
    if (skipEmpty && value is string && string.IsNullOrEmpty((string)value))
        return null;
    //1
    if (skipEmpty && value is int? && value == null)
      return null;
    //2
    if (skipEmpty && value is Guid? && value == null)
      return null;
    //....................
}

The resharper says that 1 and 2 clauses are always false. But why?

@Jaimal Chohan, no, it is not a Resharper bug. It is a perfectly valid warning. — Darin Dimitrov, Apr 01 '11 at 09:51
On the contrary @Jaimal... Resharper is right. Looks like you could do with a copy... it teaches you a lot. — spender, Apr 01 '11 at 09:52

score 6 · Accepted Answer · answered Apr 01 '11 at 09:50

6

If value is null then it is impossible to infer a type more complex than object from it, therefore it can never be int? or Guid?

answered Apr 01 '11 at 09:50

spender

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score 3 · Answer 2 · edited May 23 '17 at 12:11

3

if value is an object, and is null, what type was it? It doesn't have a type.

You've got a variable of type object, which doesn't contain anything. There's no way to know what someone else may have planned to place in that variable.

Or as the answer to C# get type of null object put it:

That's like asking what kind of cake would have been in an empty box with no label.

edited May 23 '17 at 12:11

Community

1
1

answered Apr 01 '11 at 09:49

Damien_The_Unbeliever

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score 2 · Answer 3 · answered Apr 01 '11 at 10:08

2

An is expression evaluates to true if the provided expression is non-null. Therefore, the expression (value is int? && value == null) always equals false

answered Apr 01 '11 at 10:08

vvk

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lesderid · Answer 4 · 2011-04-01T09:58:19.350

1

This should work:

if (skipEmpty && ((value is string && string.IsNullOrEmpty((string)value)) || value == null)) return null;

edited Apr 01 '11 at 09:58

answered Apr 01 '11 at 09:52

lesderid

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This should be a comment. It's not an answer. – spender Apr 01 '11 at 09:58
Indeed, changed the answer and added a comment. – lesderid Apr 01 '11 at 09:58
This should work more properly: if (value == null && skipEmpty) return null; – Alexandre Apr 01 '11 at 10:20
skipEmpty changes everything so you should evaluate it first. – lesderid Apr 01 '11 at 10:35

Nullable types in .NET

4 Answers4