How to determine if two generic type values are equal?
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comecme
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Published on 2011-01-09T13:41:21Z
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I'm trying to figure out how I can successfully determine if two generic type values are equal to each other. Based on Mark Byers' answer on this question I would think I can just use value.Equals()
where value is a generic type.
My actual problem is in a LinkedList implementation, but the problem can be shown with this simpler example.
class GenericOjbect<T> {
public T Value { get; private set; }
public GenericOjbect(T value) {
Value = value;
}
public bool Equals(T value) {
return (Value.Equals(value));
}
}
Now I define an instance of GenericObject<StringBuilder>
containing new StringBuilder("StackOverflow")
. I would expect to get true
if I call Equals(new StringBuilder("StackOverflow")
on this GenericObject instance, but I get false
.
A sample program showing this:
using System;
using System.Text;
class Program
{
static void Main()
{
var sb1 = new StringBuilder("StackOverflow");
var sb2 = new StringBuilder("StackOverflow");
Console.WriteLine("StringBuilder compare");
Console.WriteLine("1. == " + (sb1 == sb2));
Console.WriteLine("2. Object.Equals " + (Object.Equals(sb1, sb2)));
Console.WriteLine("3. this.Equals " + (sb1.Equals(sb2)));
var go1 = new GenericOjbect<StringBuilder>(sb1);
var go2 = new GenericOjbect<StringBuilder>(sb2);
Console.WriteLine("\nGenericObject compare");
Console.WriteLine("1. == " + (go1 == go2));
Console.WriteLine("2. Object.Equals " + (Object.Equals(go1, go2)));
Console.WriteLine("3. this.Equals " + (go1.Equals(go2)));
Console.WriteLine("4. Value.Equals " + (go1.Value.Equals(go2.Value)));
}
}
For the three methods of comparing two StringBuilder objects, only the StringBuilder.Equals instance method (the third line) returns true
. This is what I expected. But when comparing the GenericObject objects, its Equals() method (the third line) returns false
. Interestingly enough, the fourth compare method does return true
. I'd think the third and fourth comparison are actually doing the same thing.
I would have expected true
. Because in the Equals() method of the GenericObject class, both value
and Value
are of type T
which in this case is a StringBuilder
. Based on Mark Byers' answer in this question, I would've expected the Value.Equals()
method to be using the StringBuilder's Equals() method. And as I've shown, the StringBuilder's Equal() method does return true
.
I've even tried
public bool Equals(T value) {
return EqualityComparer<T>.Default.Equals(Value, value);
}
but that also returns false.
So, two questions here:
- Why doesn't the code return
true
? - How could I implement the
Equals
method so it does returntrue
?
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