Extending 'Normal Extensions' with 'PolyArg Extensions' & New 'club' Keyword

[sangeethnandakumar]

In C# we've normal extension methods that can accept one parameter along the "this" keyword

Existing Extension Support

public static class NormalExtensions
{
    public static bool IsAGoodBoy(this string name)
    {
        return name == 'Sangeeth';
    }
}

Then use like

var result = "Sangeeth".IsAGoodBoy();
if(result)
{
	Console.WriteLine("Hey good boy");
}

---

Proposed Improved Extension Support

The "PolyArg" Concept

The proposed "PolyArg" extension methods would allow extension method signatures to accept multiple arguments using the this keyword. For example:

public static class PolyArgExtensions
{
    public static bool IsAGoodBoyUnder24(this string name, this int val)
    {
        return name == "Sangeeth" && val < 24;
    }
}

Prerequisites

• To use this feature, the C# language might introduce a new keyword, club (Similar to "typeof," "nameof," and "stackalloc")
• This keyword would combine instances without allocation, generating new type signatures at compile-time.
• Here's how it could be used in "PolyArg" extensions:

var result = club("Sangeeth", 24).IsAGoodBoyUnder24();

if (result)
{
    Console.WriteLine("Hey young good boy");
}

Discussion Points

This proposal raises several questions and considerations:

• Do you think the "club" keyword is a good idea, and can it unlock potential future language features?
• What could be the potential implications of introducing this feature?
• Are there any conflicts with existing syntax matching that should be addressed?

Example - Using "Extension with Tuple" vs. Using "Native PolyArg Extensions" Support

To illustrate the benefits of "PolyArg" extensions, consider this comparison between the tuple approach and the proposed "club" keyword approach:

var fullName = await FetchNameFromApi();
var age = await FetchAgeFromDatabase();

// Tuple Approach (Allocates)
var result = (fullName, age).IsAGoodBoyUnder24();

// PolyArg Extension Approach using the new 'club' keyword
var result = club(fullName, age).IsAGoodBoyUnder24();

*I'd edited the discussion for better clarity

[ufcpp]

var result = ("Sangeeth", 24).IsAGoodBoyUnder24();
if (result)
{
    Console.WriteLine("Hey young good boy");
}

public static class PolyArgExtensions
{
    public static bool IsAGoodBoyUnder24(this (string name, int val) t)
    {
        return t.name == "Sangeeth" && t.val < 24;
    }
}

[sangeethnandakumar]

Right. But will it allocate a new Tuple?

[chrisoverzero]

ValueTuple, in all arities, is a value type.

[huoyaoyuan]

Value tuple is a struct and no allocation will happen.

If the extension method is trivial, it can also be inlined and the temporary struct can be treated as two normal variables.

[chrisoverzero]

This proposal raises several questions and considerations:

What’s the benefit?

[KennethHoff]

Seems like there's only 1; no allocations. And even that is wrong as the ValueTuple approach is already allocation-free.

[sangeethnandakumar]

Ya it makes sense, I'm closing the discussion. Thanks folks