For some reason C# does not allow == operator use in generic classes like here:
class Mine<T> where T : struct
{
T val;
public T Value
{
set
{
if (val == value) // Operator '==' cannot be applied to operands of type T and T happens here
{
// .. do something ...
}
}
}
}
If I replace == with val.Equals(value) I have code that works as expected but if I look at bytecode it looks much more complicated. A very simple test comparing int variables in the loop using == and Equals() showed that Equals() version was two times slower than "==" version.
I wonder if there is a way to compare primitive value types in generic classes that would be as fast as == operator. Any ideas welcome.
Edit: I got lost between timers. Performance difference is not as dramatic. Here are my latest results:
== operator 1974380 ticks
Equals() 1976358 ticks
== operator in another static function 1974604 ticks
EqualityComparer<int>.Default... 32486695 ticks
In short: Equals() is good enough.
If you are allowed to add the IEquatable<T>
constraint to the class, then you can use the IEquatable<T>.Equals(T other)
method declared in that interface:
class Mine<T> where T : struct, IEquatable<T>
{
T val;
public T Value
{
set
{
if (val.Equals(value)) //
{
// .. do something ...
}
}
}
}
The reason being that ==
defaults to reference equality and that makes no sense for value types, the answer will always be false
. Because there is no language mechanism to constrain generic types based upon static methods, the compiler simply disallows this as it can't verify that T
really has an overloaded ==
operator.
On the other hand if you constraint T
to class
it will compile just fine because reference equality does make sense for reference types.
The solution is of course IEquatable<T>
; in any sanely implemented struct IEquatable<T>.Equals(T t)
will give you value equality semantics and ==
should behave consistently.
And answering your question, no there is not. If you really need the speed of int == int
you will need to implement a non generic specialized class.
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