Creating a nullable extension method ,how do you do it?

Question

I have a situation where I need to compare nullable types.
Suppose you have 2 values:

int? foo=null;
int? bar=4;

This will not work:

if(foo>bar)

The following works but obviously not for nullable as we restrict it to value types:

public static bool IsLessThan<T>(this T leftValue, T rightValue) where T : struct, IComparable<T>
{
       return leftValue.CompareTo(rightValue) == -1;
}

This works but it's not generic:

public static bool IsLessThan(this int? leftValue, int? rightValue)
{
    return Nullable.Compare(leftValue, rightValue) == -1;
}

How do I make a Generic version of my IsLessThan?

Thanks a lot

so do you want null < 4 or null > 4 ? – Petar Ivanov Jul 03 '11 at 07:43 — Petar Ivanov, Jul 03 '11 at 07:43

Sean Thoman · Accepted Answer · 2011-07-03T07:59:18.130

23

Try this:

public static bool IsLessThan<T>(this Nullable<T> t, Nullable<T> other) where T : struct
{
    return Nullable.Compare(t, other) < 0;
}

edited Jul 03 '11 at 07:59

answered Jul 03 '11 at 07:48

Sean Thoman

7,429
6
56
103

3

You probably want to make the return read Nullable.Compare(t, other) < 0 in order to comply with the Compare documentation. The Compare method is supposed to return a value less than 0 for the "less than case". http://msdn.microsoft.com/en-us/library/dxxt7t2a.aspx – PHeiberg Jul 03 '11 at 07:57
@SeanThoman .Thank you.It works.I did write what you suggested but didnt work ,I must have written something different.thanks – user9969 Jul 03 '11 at 08:12
1

I am getting exception message saying "The type 'T' must be a non-nullable value type in order to use it as parameter 'T' in the generic type or method 'Nullable'." – Kasim Husaini Dec 30 '18 at 07:03
@KasimHusaini how did you solve that error ? – Mauricio Gracia Gutierrez Feb 08 '22 at 22:05
1

@MauricioGraciaGutierrez, I wasn't able to fix the issue. – Kasim Husaini Feb 22 '22 at 10:59
compiler says that C# 9.0 must be used in order to allow that syntax. – Mauricio Gracia Gutierrez Feb 22 '22 at 14:46

score 2 · Answer 2 · answered May 18 '17 at 19:35

2

It can be simplified:

public static bool IsLessThan<T>(this T? one, T? other) where T : struct
{
    return Nullable.Compare(one, other) < 0;
}

answered May 18 '17 at 19:35

Giovani

21
1

you will need C# version 9.0 for this to work – Mauricio Gracia Gutierrez Feb 08 '22 at 22:11

Creating a nullable extension method ,how do you do it?

2 Answers2

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