How to compare nullable types?

问题

I have a few places where I need to compare 2 (nullable) values, to see if they're the same.

I think there should be something in the framework to support this, but can't find anything, so instead have the following:

public static bool IsDifferentTo(this bool? x, bool? y)
{
    return (x.HasValue != y.HasValue) ? true : x.HasValue && x.Value != y.Value;
}

Then, within code I have if (x.IsDifferentTo(y)) ...

I then have similar methods for nullable ints, nullable doubles etc.

Is there not an easier way to see if two nullable types are the same?

Update:

Turns out that the reason this method existed was because the code has been converted from VB.Net, where Nothing = Nothing returns false (compare to C# where null == null returns true). The VB.Net code should have used .Equals... instead.

回答1:

C# supports "lifted" operators, so if the type (bool? in this case) is known at compile you should just be able to use:

return x != y;

If you need generics, then EqualityComparer<T>.Default is your friend:

return !EqualityComparer<T>.Default.Equals(x,y);

Note, however, that both of these approaches use the "null == null" approach (contrast to ANSI SQL). If you need "null != null" then you'll have to test that separately:

return x == null || x != y;

回答2:

Nullable.Equals<T>?

回答3:

if (x.Equals(y))

回答4:

You can use the static Equals method on System.Object:

var equal = object.Equals(objA, objB);

回答5:

Use Compare:

http://msdn.microsoft.com/en-us/library/dxxt7t2a.aspx

回答6:

Just use ==, or .Equals().

来源：https://stackoverflow.com/questions/2341660/how-to-compare-nullable-types

标签

extension-methods

nullable