This code snippet works as expected for the int type:

public class Test { public int Value { get => _Value; set { if (_Value != value) _Value = value; } } private int _Value; }

When int is replaced by the generic T, the compiler complains with:

Operator '!=' cannot be applied to operands of type 'T' and 'T'

Why does this happen and is there a way to solve it?

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3 Answers

using System.Collections.Generic; public class Test<T> { public T Value { get => _Value; set { // operator== is undefined for generic T; EqualityComparer solves this if (!EqualityComparer<T>.Default.Equals(_Value, value)) { _Value = value; } } } private T _Value; }
8

T is a type argument and can be a class or a struct, Thus the compiler won't let you perform actions that don't exist both in classes and structs.

structs don't have the == and != by default(but can be added), this is why the compiler complains.

If you use the where keyword to add a constraint to the type argument, the compiler will let you use that type\interface method\operators

constrain T to be a class

public class Test<T> where T : class { public T Value { private T _Value; get { return _Value; } set { if (_value != value) _Value = value; } } }

Or simply use Equals instead of the == operator

public class Test<T> { public T Value { private T _Value; get { return _Value; } set { if (!_value.Equals(value) _Value = value; } } }
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T can be any type. You cannot use ==/!= on structs, unless such operators are defined on the (struct) type.

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