What is the difference between new Object() and new Object{} in expressions in C#

Question

I have the following code snippet:

Expression<Func<TSource, TDest>> expression = model => new TDest{}; // Result: {model => new TestModel(){}} 

ReSharper refactors this snippet with RedundantEmptyObjectOrCollectionInitializer setting:

Expression<Func<TSource, TDest>> expression2 = model => new TDest(); // Result: {model => new TestModel()} 

After that, my code doesn't work. What influence do the curly braces have on initializing?
I found What is the Difference Between new object() and new {} in C#? on Stack Overflow, but both instances look equal.

expression.GetType().ToString() is equal to expression2.GetType().ToString()

What is the difference between these initializations in expression trees?:

var a = model => new TDest{}; var b = model => new TDest(); 

Answer 1

In regular raw C# the answer would be "nothing". However, when you involve expression trees, there is a difference; as can be seen here

using System; using System.Linq.Expressions; public class C<TSource, TDest> where TDest : new() {     public Expression<Func<TSource, TDest>> Foo() => model => new TDest();     public Expression<Func<TSource, TDest>> Bar() => model => new TDest {}; } 

compiles as:

public Expression<Func<TSource, TDest>> Foo() {     ParameterExpression parameterExpression = Expression.Parameter(typeof(TSource), "model");     Expression arg_2E_0 = Expression.New(typeof(TDest));     ParameterExpression[] expr_2A = new ParameterExpression[1];     expr_2A[0] = parameterExpression;     return Expression.Lambda<Func<TSource, TDest>>(arg_2E_0, expr_2A); }  public Expression<Func<TSource, TDest>> Bar() {     ParameterExpression parameterExpression = Expression.Parameter(typeof(TSource), "model");     Expression arg_38_0 = Expression.MemberInit(Expression.New(typeof(TDest)), Array.Empty<MemberBinding>());     ParameterExpression[] expr_34 = new ParameterExpression[1];     expr_34[0] = parameterExpression;     return Expression.Lambda<Func<TSource, TDest>>(arg_38_0, expr_34); } 

So one of them involves an Expression.MemberInit (with an empty set of MemberBinding elements) in addition to Expression.New. This can upset any LINQ provider (or any similar expression-tree analysis) that doesn't expect it.