positional record can't accept Attribute.

[moh-hassan]

Records with attributes can be declared as

record Point 
{
    [Option]
    public int X { get; }
    [Option]
    public int Y { get; }
}

Nominal record can be declared as:

record Point(int X, int Y);

Trying to add attribute, like

record Point([Option]int X, [Option]int Y); //invalid syntax

Compiler raise an exception:

CS0592 Attribute 'Option' is not valid on this declaration type. It is only valid on 'property, indexer' declarations.

As I see from this doc, there is no limitation on the nominal record.
I'm using Net 5 Preview 5.
How to define attributes for the nominal record?

[YairHalberstadt]

Perhaps there should be a [property: Option] syntax similar to the existing [field: Option] syntax for auto properties?

[moh-hassan]

@YairHalberstadt ,
How your syntax match the proposal(now it is implemented) of Nominal records.
Attributes are allowed for positional records but not for Nominal records.

[333fred]

@moh-hassan, you seem to be confusing nominal and positional records. This syntax is a nominal record:

record Point 
{
    [Option]
    public int X { get; }
    [Option]
    public int Y { get; }
}

This is a positional record:

record Point(int X, int Y);

Yair is proposing an additional attribute scope, presumably something like

record Point([property: Option]int X, [property: Option]int Y);

for the positional case.

[moh-hassan]

Thanks @333fred for clarification.

[RikkiGibson]

See dotnet/roslyn#44691. I believe the expectation is that attributes will go on the parameter by default but if a property: target is specified we will put them on the synthesized property instead. This will require a diagnostic in the case that no property is synthesized for the positional parameter (like when the property is explicitly declared in the record body).

[moh-hassan]

Net 5 version 5.0.100-rc.1.20452.10 is now supporting positional record with attributes as described by @YairHalberstadt

public record Test(
    [field: A]
    [property: B]
    [param: C]
    [D]     
    [property: Option]
    int P1
    )
{
}

[333fred]

@moh-hassan is there anything else you were requesting? Or can this be closed?

[moh-hassan]

@333fred ,
Just, I want to do more checks for the feature using Net5 Rc1.
Although VScode IDE didn't show any compilation warning, I was surprised to get a compilation warning after cleaning for the field and property attributes, but passed for [param ] and [D].
I'll feed back when test is completed.

[moh-hassan]

I can confirm that attributes for positional record are implemented in 5.0.100-rc.1.20452.10. No compilation warning in VScode and I can access the attributes at runtime:

The attributes for the member 'Int32 P1' are:
The type of the attribute is 'B'.
The type of the attribute is 'CommandLine.OptionAttribute'.

@333fred
Thanks,
You can close this issue.