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Question

Is it expected behavior with records in C#10?

Console.WriteLine(new Derived1()); // =output=> Derived1 { }
Console.WriteLine(new Derived2()); // =output=> Base

record Base
{
    public override string ToString() => "Base";
}

record Derived1 : Base;

record Derived2 : Base
{
    public override string ToString() => base.ToString();
}

Answer 1

Yes, it is. Compiler will automatically generate formatting for display by overriding ToString for every record:

Record types have a compiler-generated ToString method that displays the names and values of public properties and fields. The ToString method returns a string of the following format:

<record type name> { <property name> = <value>, <property name> = <value>, ...}

unless you override it yourself (as you do in Derived2 and Base ).

See the sharplab.io decompilation.

Also note next:

In C# 10 and later, your implementation of ToString may include the sealed modifier, which prevents the compiler from synthesizing a ToString implementation for any derived records.

So if your base implementation is sufficient you can just seal it to prevent compiler from generating overrides:

record Base
{
    public sealed override string ToString() => "Base";
}