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Impress your colleagues with your knowledge about..the PrintMembers method

Sometimes when working with C# you discover some hidden gems. Some of them very useful, other ones a little bit harder to find a good way to benefit from their functionality. One of those hidden gems that I discovered some days ago is the PrintMembers method.

Record Types

To explain where you can find this method, I first have to talk about record types.  Record types were introduced in C# 9 as a new reference type that you can create instead of classes or structs. C# 10 adds record structs so that you can define records as value types.

Records are distinct from classes in that record types use value-based equality. Two variables of a record type are equal if the record type definitions are identical, and if for every field, the values in both records are equal.

Record types have a compiler-generated ToString method that displays the names and values of public properties and fields:

Person{ FirstName = Bart, LastName = Wullems }

In an application we are building we are using this ToString() method to generate a cache key. This works great until you add another reference type to your record type:

If we now print out the value, we see the following:

Product { FirstName = Bart, LastName = Wullems, PhoneNumbers = System.String[] }

We no longer have uniqueness what doesn’t make it a good cache key anymore.

PrintMembers

Let’s fix this by implementing a PrintMembers method on our record type.

Important! If you want to do this,  you need to be aware about the following:

  • For a sealed record that derives from object (doesn't declare a base record): private bool PrintMembers(StringBuilder builder);
  • For a sealed record that derives from another record (note that the enclosing type is sealed, so the method is effectively sealed): protected override bool PrintMembers(StringBuilder builder);
  • For a record that isn't sealed and derives from object: protected virtual bool PrintMembers(StringBuilder builder);
  • For a record that isn't sealed and derives from another record: protected override bool PrintMembers(StringBuilder builder);

Here is the implementation for our Person class:

If we now print out the value,  all the values are included:

Product { FirstName = Bart, LastName = Wullems, PhoneNumbers = 123/45.67.89,987/65.43.21 }

Nice!

More information:

Records - C# reference | Microsoft Learn

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