CODEWITHSUNDEEP
c#
rudimenter
rudimenter

Reputation: 3450

Comparing NaN and null returns illogic value

Why does the following code snippet returns 1:

double i = double.NaN;
double? i2 = null;
i.CompareTo(i2);

From my point of view it makes no sense. An Exception would be more appropriate.

What do you think was the reasoning behind the decision.

Upvotes: 7

Views: 775

Answers (3)

Ilya Ivanov
Ilya Ivanov

Reputation: 23626

When you decompile CompareTo of double, you can see:

public int CompareTo(object value)
{
  if (value == null)
    return 1;

just to put null elements at the bottom of any sorted sequence.

Upvotes: 2

DGibbs
DGibbs

Reputation: 14618

From the documentation on CompareTo:

The value parameter must be null or an instance of Double; otherwise, an exception is thrown. Any instance of Double, regardless of its value, is considered greater than null.

The value parameter in your example is null. NaN is therefore considered greater than null which is why CompareTo correctly returns 1.

Upvotes: 3

JLRishe
JLRishe

Reputation: 101680

From the MSDN documentation on IComparable.CompareTo():

By definition, any object compares greater than (or follows) null, and two null references compare equal to each other.

This is also apparent from the Double.CompareTo(object) documentation:

Returns a positive integer if This instance is greater than value. -or- This instance is a number and value is not a number (NaN). -or- value is a null reference (Nothing in Visual Basic).

As Adam Houldsworth points out, if something.CompareTo(somethingElse) threw an exception when somethingElse is null, then sorting and things like that would require lots of extra exception handling.

Upvotes: 2

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