Object Initialization Property Extension to Returned Objects

[hawkerm]

This would be a re-use of the object initialization syntax beyond constructors for returned objects from methods. Would be similar to with with record types as well, I suppose.

Not sure how best to describe this, but it's something I always want to do when I get back objects from factories or other built-in API surfaces which return settings style objects that I'm trying to modify.

e.g. here's a scenario from the Windows API as an example customizing a bunch of paragraph settings from the ITextParagraphFormat interface:

    var paragraphFormat = TextDocument.GetDefaultParagraphFormat();
    paragraphFormat.SpaceBefore = 24;
    paragraphFormat.SpaceAfter = 24;

    TextDocument.SetDefaultParagraphFormat(paragraphFormat);

What I'd prefer to do instead like if I had constructed this object is the following:

    var paragraphFormat = TextDocument.GetDefaultParagraphFormat() {
        SpaceBefore = 24,
        SpaceAfter = 24,
    };

    TextDocument.SetDefaultParagraphFormat(paragraphFormat);

This saves me from having to retype the variable name, or copy-paste a whole wall of text for increasing number of properties. Instead, the value of the object is more easily seen and grouped in a familiar construct.

    var newThing = SomeFactory.GetNewBlankFoo() {
       ConfigValue = 42,
       Name = "Bar",
       Timing = new(4.5),
       Alignment = Alignment.Right,
       WhatElse = "more...",
    };

    newThing.Execute();

This works well with the factory pattern as well, as sometimes that's the only way to get a 'new' construction of an object with some API surfaces, as a developer though I frequently want to modify those outcomes before use. Being able to use a familiar pattern I use for construction of other types would be a great feeling and shortcut to my productivity. Thanks!

[ufcpp]

https://github.com/dotnet/csharplang/blob/main/meetings/2020/LDM-2020-04-20.md

[hawkerm]

Thanks for the reference to a relevant discussion. I can see the concern with it only being for new objects. But I'd be equally happy with with and extending it beyond records as well, e.g.

    var paragraphFormat = TextDocument.GetDefaultParagraphFormat() with {
        SpaceBefore = 24,
        SpaceAfter = 24,
    };

Though, I think the question is would with be returning a second copy of the original return value or a modified instance of it. As it'd be more efficient in these cases to modify the original. With records, it's always a new 'instance' effectively, right?