New "dependency" keyword

[ekisielinski]

Instead of this:

public class MyService
{
    IServiceA serviceA;
    readonly IServiceB serviceB;
    IServiceC? serviceC;

    public MyService( IServiceA serviceA, IServiceB serviceB, IServiceC? serviceC )
    {
        if (serviceA is null) thrown new ArgumentNullException(...);
        this.serviceA = serviceA;        
        if (serviceB is null) thrown new ArgumentNullException(...);
        this.serviceB = serviceB;        
        this.serviceC = serviceC; // nullable, no checking for null
    }
}

We could write this:

public class MyService
{
    dependency IServiceA serviceA;
    dependency readonly IServiceB serviceB;
    dependency IServiceC? serviceC;
}

Constructor would be created by compiler with dependencie with the same order as declared.

Additionaly we could create method:

private void ValidateDependencies()
{
     // additional checking
}

Which would be called in auto-generated constructor.

:)

[HaloFour]

With records you will be able to do this:

public record MyService(IServiceA serviceA, IServiceB serviceB, IServiceC serviceC) {
    // members go here
}

It's expected that primary constructors (the feature that allows for a parameter list to be specified after the type name) will be supported for normal classes by C# 10.0 complete with a constructor block where you can perform validation:

public class MyService(IServiceA serviceA, IServiceB serviceB, IServiceC serviceC) {
    public MyService {
        if (serviceA is null) throw new ArgumentNullException(...);
        if (serviceB is null) throw new ArgumentNullException(...);
    }

    // members go here
}

With #2145 you could possibly also write it as:

public class MyService(IServiceA serviceA!!, IServiceB serviceB!!, IServiceC serviceC) {
    // members go here
}

[PathogenDavid]

This feels like a very domain-specific problem that would be better solved with a domain-specific source generator.

[Richiban]

It's definitely not domain-specific, although it might be coding style-specific.