C# Constructor Shorthand

[TropicalThunder]

Much like the Typescript language, it would be nice to get rid of the tedious writing of constructors when using dependency injection.

Today I will write something like:

public class TestClass
{
	private readonly DatabaseContext _context;

	public TestClass(DatabaseContext context)
	{
		_context = context;
	}  
}

My suggestion is that we could write something like this in the future:

public class TestClass
{
    public TestClass(private DatabaseContext context) { }  
}

[canton7]

This looks similar to records. See #3231, #3226, #3213, #3170, #3146, #3137, #2750, #2699, #2691, #1667, and many more besides.

[TropicalThunder]

This looks similar to records. See #3231, #3226, #3213, #3170, #3146, #3137, #2750, #2699, #2691, #1667, and many more besides.

The others propose several other large and more comprehensive changes whereas this is much more specific, and that ought to be looked at for the future.

[DavidArno]

Those other "large and more comprehensive changes" completely cover what you are proposing here though. So this is just a syntax variation on what is already in planning for v9. So this is really just a duplicate request.

[TropicalThunder]

So this is just a syntax variation on what is already in planning for v9.

That I did not know. Thanks! All I am saying is that something has to be done.

[Richiban]

This is not records but primary constructors, which also have their own proposal. #2691

[canton7]

@Richiban Eh, primary constructors let you say:

public class C(int i, string s)
{
    ...
}

which isn't what this issue says. The idea of primary constructors is an older one which sort of got subsumed into the records proposal, if I'm following things correctly. #2691 is in the list of issues I gave as references, either way.

[Richiban]

@canton7 The syntax is slightly different, but the feature is the same--my class has a dependency (a field), let me write it once in such a way that it gets set in a constructor.

Records are a quick and clean way of defining a class with value equality and, depending on which version of records you go for, an auto-generated constructor.

[canton7]

@Richiban They keep humming and harring about whether value equality is part of records, or its own separate thing. I think it's safe to say that all discussion around the idea of "let me declare all of these properties, and a constructor to assign to them, with minimal effort" come under the heading of "Records" these days.

[yulObraz]

It looks like I hate the records already... The records as I understude are structures with simplified construction. I am not so deep in the language specification to say something about theese things. I have't felt necessity in them. But I need a simplified construction of complex class with DI. Surely I will never compare the classes by theese properties. So a vary important problem of records is not important in this case.

[OskarKlintrot]

@yulObraz Records are a quick and easy way to write DTO classes and has nothing to do with this issue. This issue is to get the same shorthand that Typescript has. I think records are inspired from F#.

[Richiban]

It now seems pretty possible that C# will get primary constructors (ironically enough they talk about it in a records LDM notes: https://github.com/dotnet/csharplang/blob/master/meetings/2020/LDM-2020-04-27.md)

[Richiban]

Primary constructors will allow something similar to this:

public class C(ServiceA a, ServiceB b)
{
	public void M()
	{
		a.DoSomething();
		b.DoSomethingElse();
	}
}

[YairHalberstadt]

Closing, as this is being considered as part of the discussion surrounding primary constructors: #2691