C#•2w ago

records, with expression, required property

I'm hitting a strange behaviour and not sure if it's intended. I have the following record definition:

public record Options
{
    public required IDataSource DataSource { get; init; }

    public int? Take { get; init; } = null;
}

public record Options
{
    public required IDataSource DataSource { get; init; }

    public int? Take { get; init; } = null;
}

Then I use it in code like this:

var config = new Options() { DataSource = new DataSource(), }
assert(config.DataSource is null) // false
var config2 = config with { Take = null };
assert(config2.DataSource is null); // true
var config3 = config with { Take = null, DataSource = config.DataSource };
assert(config3.DataSource is null); // false

var config = new Options() { DataSource = new DataSource(), }
assert(config.DataSource is null) // false
var config2 = config with { Take = null };
assert(config2.DataSource is null); // true
var config3 = config with { Take = null, DataSource = config.DataSource };
assert(config3.DataSource is null); // false

Why is config2.DataSource null? Is this intended behaviour of combining required and with? If so, shouldn't I get a warning/error that I have an uninitialised required property in config2?

12 Replies

canton7•2w ago

Can't repro?

MODiX•2w ago

canton7

REPL Result: Success

var config = new Options() { DataSource = "DS" };
Console.WriteLine(config.DataSource is null); // false
var config2 = config with { Take = null };
Console.WriteLine(config2.DataSource is null); // true
var config3 = config with { Take = null, DataSource = config.DataSource };
Console.WriteLine(config3.DataSource is null); // false

public record Options
{
    public required string DataSource { get; init; }

    public int? Take { get; init; } = null;
}

var config = new Options() { DataSource = "DS" };
Console.WriteLine(config.DataSource is null); // false
var config2 = config with { Take = null };
Console.WriteLine(config2.DataSource is null); // true
var config3 = config with { Take = null, DataSource = config.DataSource };
Console.WriteLine(config3.DataSource is null); // false

public record Options
{
    public required string DataSource { get; init; }

    public int? Take { get; init; } = null;
}

Console Output

False
False
False

False
False
False

Compile: 514.274ms | Execution: 108.868ms | React with ❌ to remove this embed.

seky16OP•2w ago

here's my repro case, it's a bit more complicated

TC.zip

333fred•2w ago

Can you please just share code directly, rather than asking us to download zip files? You can use $paste if it's longer

MODiX•2w ago

If your code is too long, you can post to https://paste.mod.gg/, save, and copy the link into chat for others to see your shared code!

333fred•2w ago

Because I'm not downloading a zip file from a random discord user, sorry

seky16OP•2w ago

https://github.com/seky16/record-tc/blob/master/WebAPI/Handler.cs Not sure if it's inheritance or the IsExternalInit hack that's causing the trouble

MODiX•2w ago

333fred

REPL Result: Success

InheritedOptions config = new InheritedOptions()
{
    DataSource = new EmptySource()
};

if (config.DataSource is null)
    throw new InvalidProgramException(); // doesnt happen

var config2 = config with { Take = null, };

if (config2.DataSource is null)
    throw new StackOverflowException(); // shouldnt happen

Console.WriteLine("Wasn't null");

public interface IDataSource;
public interface ISet;

public class EmptySource : IDataSource;

public record Options : IDataSource
{
    public required IDataSource DataSource { get; init; }

    public int? Take { get; init; } = null;
}

internal record InheritedOptions : Options
{
    public ISet? Set { get; init; }
}

InheritedOptions config = new InheritedOptions()
{
    DataSource = new EmptySource()
};

if (config.DataSource is null)
    throw new InvalidProgramException(); // doesnt happen

var config2 = config with { Take = null, };

if (config2.DataSource is null)
    throw new StackOverflowException(); // shouldnt happen

Console.WriteLine("Wasn't null");

public interface IDataSource;
public interface ISet;

public class EmptySource : IDataSource;

public record Options : IDataSource
{
    public required IDataSource DataSource { get; init; }

    public int? Take { get; init; } = null;
}

internal record InheritedOptions : Options
{
    public ISet? Set { get; init; }
}

Console Output

Wasn't null

Wasn't null

Compile: 585.355ms | Execution: 99.468ms | React with ❌ to remove this embed.

333fred•2w ago

Alright, so this is something with your multi-targeting If I switch your Expressions project to net8.0, it works fine

333fred•2w ago

@seky16 looks like we have an existing bug on this, https://github.com/dotnet/roslyn/issues/72357. Can you add a comment to ping the issue again?

GitHub

Issues · dotnet/roslyn

The Roslyn .NET compiler provides C# and Visual Basic languages with rich code analysis APIs. - Issues · dotnet/roslyn

333fred•2w ago

Good news @seky16, you nerd sniped me into fixing this: https://github.com/dotnet/roslyn/pull/76347

GitHub

Do not bail generating base type initializer in the presence of use...

We were returning early from generating a call to the base record copy constructor initializer if use site diagnostics reported any kind of diagnostic, including warnings. This isn't good i...

seky16OP•2w ago

thanks! yeah workaround with targeting net8.0 works, so that's great

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records, with expression, required property