Inline Interfaces junction

[BYTESHAUS]

Fine-granulated interfaces and their multi-inheritance into more substantial belong to sound design practices.

However, it may lead to a combinatory explosion. Suppose there are ISelectable, ITimestamped, and INotifyPropertyChanged, which combinations imply 23 nominal declarations.

What if this could be achieved with [IInterfaceA, IInterfaceB[, IInterfaceC_[, ...]_]>

Syntax sketch:

static class AircraftBuilder
{
// as return
        static [IAirSpecs, IPowerplant] BusinessJet(...) { ... }
        static [IAirSpecs, IPowerplant, ILoadSpecs] Cargo(...) { ... }
        static [IAirSpecs, IPowerplant, ILoadSpecs, IPassengerConfig] Liner(...) { ... }
}

// as arguments
IList<IataAirportCode> Planning.Destinations.FindOptimal(IataAirportCode from, [IAirSpecs, IPowerplant] vehicle) { ... }
void Planning.Capacity.Register([ILoadSpecs, IPassengerConfig] transport) { ... }

The enclosing syntax is a proposal and the subject to discuss.

[ufcpp]

see #399

[BYTESHAUS]

Thanks for the fast feedback but my idea is a bit different than type unions which require definition.

…

________________________________ From: Nobuyuki Iwanaga ***@***.***> Sent: Monday, May 19, 2025 1:19 PM To: dotnet/csharplang ***@***.***> Cc: Kyrill 🎼D♭ ***@***.***>; Author ***@***.***> Subject: Re: [dotnet/csharplang] Inline Interfaces junction (Discussion #9395) see #399<#399> — Reply to this email directly, view it on GitHub<#9395 (comment)>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/AOTRIHGZ4FFCPXK62GFG4Y327G42ZAVCNFSM6AAAAAB5NKOSZ6VHI2DSMVQWIX3LMV43URDJONRXK43TNFXW4Q3PNVWWK3TUHMYTGMJZGI3DANI>. You are receiving this because you authored the thread.Message ID: ***@***.***>

[HaloFour]

That proposal covers both declared and "ad hoc" unions and intersections. It's more about the concept than any specific syntax to implement such a feature.