when I am writing in c# (on .net 5) the following code

public class Apple
{
    public int weight { get; set; }
    public Apple(int w)
    {
       weight = w;
    }

    public bool Equals(Apple other)
    {
        return ((other != null) &&(weight == other.weight));
    }
}

in the main function, I declare

Apple a1 = new Apple(10);
Object a2 = new Apple(10);

when I run afterwards the following code Console.WriteLine(a1.Equals(a2)); it will compile and run and return "false" (even though they are the same).

but writing this code a1 = a2; will get a compiler error.

Error CS0266 Cannot implicitly convert type 'object' to 'Apple'. An explicit conversion exists (are you missing a cast?)

can anyone explain what is the difference?

CodePudding user response：

Every object already has an bool Equals(object? obj) method, and you're calling that when you pass an object to your Equals. Instead properly override the built-in Equals

public class Apple
{
    public int weight { get; set; }
    public Apple(int w)
    {
        weight = w;
    }

    public override bool Equals(object? obj)
    {
        if (obj is Apple a )
        {
            return this.weight == a.weight;
        }
        return false;
    }
    public override int GetHashCode()
    {
        return HashCode.Combine(weight);
    }

}