[Proposal] Spread members into anonymous object creation #10039

iikuzmychov · 2026-03-12T01:12:28Z

iikuzmychov
Mar 12, 2026

Allow spreading members of an existing object into anonymous object creation.

var bookWithAuthor = new
{
    Author = "Frank Herbert",
    ..book
};

Equivalent to writing out the included members explicitly:

var bookWithAuthor = new
{
    Author = "Frank Herbert",
    book.Title,
    book.Pages
};

Today the options are either nesting:

var bookWithAuthor = new
{
    Author = "Frank Herbert",
    Book = book
};

or repeating all members manually:

var bookWithAuthor = new
{
    Author = "Frank Herbert",
    book.Title,
    book.Pages
};

The first changes the shape. The second is verbose and brittle.

Support spread syntax in anonymous object creation:

var x = new
{
    A = 1,
    ..obj
};

Equivalent to:

var x = new
{
    A = 1,
    obj.P1,
    obj.P2,
    obj.P3
};

Example:

var x = new
{
    Title = "Override",
    ..book
};

If book also contains Title, this is a compile-time error.