casting string to IEquatable

Question

while trying to compile following code

IEquatable<Object> value = "test";

it causes this error:

Cannot implicitly convert type 'string' to 'System.IEquatable<object>'

but string implements IEquatable<String>

MyCode:

    public class Equals : Validation
    {
        public IEquatable<Object> Value { get; set; }

        public Equals(IEquatable<Object> value)
        {
            Value = value;
        }

        public override bool Validate(Object value)
        {
            return Value.Equals(value);
        }
    }

Usage

        [Equals("test")]
        public string Name { get; set; }

Google Covariance and Contravariance and you should find all the info you need or check out this https://stackoverflow.com/questions/9806170/covariance-and-contravariance-in-c-sharp — Dave, Jan 21 '19 at 14:14
@Sahandevs It doesn't mean that casting the generic type would be safe. Let's take a simple example: `List`. By following your reasoning, it should be castable to `List — Kevin Gosse, Jan 21 '19 at 14:18
@Sahandevs what's your real problem ? what do you need `IEquatable — Ahmad Ibrahim, Jan 21 '19 at 14:21
In this precise case, you don't need `IEquatable`. Just store an `Object` and call `Equals(object)` : https://learn.microsoft.com/en-us/dotnet/api/system.object.equals — Kevin Gosse, Jan 21 '19 at 14:32
@KevinGosse but in case of Max Or Min there is no compareTo method for object and i have to use IComparable — Sahandevs, Jan 21 '19 at 14:34
This is fundamentally unsafe, if it were allowed you could do: `IComparable — Lee, Jan 21 '19 at 14:43

score 1 · Accepted Answer · answered Jan 21 '19 at 14:14

1

String implements IEquatable<String> and not IEquatable<Object> So IEquatable<String> value = "test" should work

answered Jan 21 '19 at 14:14

Merhat Pandzharov

175
7

i cannot change the generic type is there anyway to convert these two? string can be casted to object – Sahandevs Jan 21 '19 at 14:16
No it is not possible. You can cast string to object but you cant cast `IEquatable` to `IEquatable – Merhat Pandzharov Jan 21 '19 at 14:19

score 0 · Answer 2 · answered Jan 21 '19 at 14:36

0

for your code to work, you can not insert into an object the value of a string so that it works use:

IEquatable<string> value ="test";

answered Jan 21 '19 at 14:36

rafael3do

1
2

2 Answers2