Develop Reference

What does "initializing an instance of a class" mean?

After reading Meanings of declaring, instantiating, initializing and assigning an object it talks about what initializing a variable means. But it doesn't explain what "initializing" an instance of a class means.
public class Test
{
public static void Main()
{
Person person1 = new Person();
}
}
public class Person
{
// body
}
What does it mean to initialize an instance of a class?

Yeah, I don't like the "initialize" of the linked answer so much either, because it really only talks about giving a value to a single variable and doesn't really draw any distinctions between instantiation and assignment (the same lines of code are found in all of them) so for me it's a bit vague. We do have more specific processes (especially these days of modern c# syntax) when we talk about initialization
Initialize usually means "to give a created instance some initial values". Your class Person has nothing to initialize, so you could say that just by making it anew(instantiating) you've also done all the initialization possible and it's ready for use
Let's have something we can set values on
public class Person{
public string Name {get;set;}
public string Address {get;set;}
public Person(string name){
if(name == null) throw new ArgumentNullException(nameof(name));
Name = name;
}
}
Initializing as part of construction:
p = new Person("John");
Constructors force us to supply values and are used to ensure a developer gives a class the minimum set of data it needs to work.. a Person must have a name. Address is optional. We have created a person with the name initialized to John
Initializing post construction
You can give an instance additional (optional) values after you construct it, either like
p = new Person("Bill");
p.Address = "1 Microsoft Way";
Or
p = new Person("Bill"){
Address = "1 Microsoft Way"
}
Which is a syntactic sugar the compiler unrolls to something like the first. We refer to everything in the { } brackets of the second example as "an object initializer". An important distinction here though is that the first form (p.Address=...) is not considered to be initialization by the compiler. If you made the address property like:
public string Address {get;init;}
Then it can only be set in a constructor or in an object initializer, which is the latter form above. The p.Address=... form would result in a compiler error if the property were declared with init
Props set just after construction are part of the initialization process (as an English/linguistic thing) though I wouldn't call it init if it was any further down the line, such as
p = new Person("Sam");
string addr = Console.ReadLine();
p.Address = addr; //not initialization
You might find cases where people talk about initialization in the sense for "the first time a variable or property is given a value" but that's also more a linguistic/English thing than a c# thing
The compiler knows how to perform other initialization, so we also call things like this "an initializer":
string[] x = new string[] {"a","b","c"};
The process of giving the array those 3 values is initialization, and the compiler will even take the type of the first argument and use it to make the array type, so an array can be type declared and ignited from the data:
var x = new[] {"a","b","c"};

Is Object Literal Instantiation faster than setting properties? [duplicate]

This question already has answers here:
.NET object creation, whats faster?
(4 answers)
Closed 6 years ago.
Given the following example, is one objectively better/faster/safer than the other? Should object literal instantiation be a best practice where it is practical?
Where is this inappropriate?
class Person
{
public string name;
public int age;
}
void MakePeople()
{
Person myPerson = new Person();
myPerson.name = "Steve";
myPerson.age = 21;
Person literalPerson = new Person { name = "John", age = 22 };
}

No, it isn't faster or slower. It is the same.
The compiler translates object initializers to a constructor call followed by setting those properties.
Person literalPerson = new Person { name = "John", age = 22 };
Turns to:
Person myPerson = new Person();
myPerson.name = "John";
myPerson.age = 22;
You should use what is more readable and what you have agreed on with your team.

Either is appropriate. It depends on what you need to do to set properties. For example, I would avoid literal instantiation in cases where some logic is needed to arrive at a property value:
Person myPerson = new Person();
myPerson.SomeProperty = if IsNewPerson ? GetPropertyFromDatabase() : GetDefaultProperty();
Edit:
One advantage to using literal object initialization in Visual Studio is that Intellisense will prompt for properties, showing only those which have not already been declared. (I've ran into code where a value was redundantly assigned when setting properties.)

If you take a look at the IL that is generated, I'm pretty sure you'll find that they are identical. Using object initializers is just a compiler shortcut.

I don't think speed should be what drives this decision. There is probably very little difference between the speed of either method.
I think code readability should be the prime factor in which way you go. Using that criteria, I think they are very close and it comes down to personal preference or whatever your team decides on. However, I think in the case of a object with requires many properties to be set, explicitly calling setters is a little more readable.

Use of var and default for declaration in C#

Recently I saw a person heavily using var and default keywords for declaration of variables (and for every declaration), something like this:
var employee = default(Employee); //Employee is a class
var errorInfo = default(ErrorInfo); //ErrorInfo is struct; Blank is default value
var salary = default(Double);
var isManager = default(Boolean?);
instead of using:
Employee employee = null; //Employee is a class
ErrorInfo errorInfo = Blank; //ErrorInfo is struct; Blank is default value
Double salary = 0.0;
Boolean? isManager = null;
or, instead of using even:
Employee employee; //Employee is a class
ErrorInfo errorInfo; //ErrorInfo is struct; Blank is default value
Double salary;
Boolean? isManager;
Now using var and default for declaration for every variable is something i am not accustomed to.
Want to know:
- If this is a recommended practice?
- Your views and preference?
PS:
- Have gone through Use of var keyword in C#, Use of "var" type in variable declaration and https://stackoverflow.com/questions/633474/c-do-you-use-var, however, think that this question although related is slightly different as it is solely around declaration/initialization and not around assignment.
- I understand the difference between snipped 2 and snippet 3. However, question is more around snippet 1.
- If you strongly feel that this question belongs to programmers stackexchange feel free to move.

I'm not going to say anything about "var" there have been comments and discussions about this in the past (sufficiently so ;-)
Concerning "default()" I would not use this to initialize a known type, but rather only in generics. There it helps to transparently handle value types or reference types by allowing you to provide a default (return) value or can be used in comparisons.

Well, the default keyword isn't the most used keyword I think, and in my opinion it serves its purpose best in terms of Generics, like so:
public class Foo<T>{
private T _instance;
public Foo<T>(){
_instance = default(T);
}
}
in order to get a new default instance of T.
There are really no reasons to use it like scenario 1 in your post.
Using var however is a different question, and many view this as a matter of readability. I default to var when I write code simply because I find it easier to read:
var me = new Person();
It seems a bit redundant in terms of readability to do
Person me = new Person();
Another case I recommend var is if something changes. Consider the following example:
public decimal Calculate(decimal one, decimal two){
return one + two;
}
And somewhere else in your code:
decimal d = Calculate(1M, 2M);
If you for some reason change the return type of Calculate to, say, double you need to change all the places where you strongly defined the variable.
If you instead do
var d = Calculate(1M, 2M)
you don't have to worry about this. The Double/Decimal example is a bit simple, but in terms of refactoring and interfacing out classes, I've found this very useful.

I think this is bad practice which will prevent the compiler (and 3rd party tools) from catching bugs related to failure to initialize a variable. Generally I try to keep declaration and assignment as close to each other as possible. Assigning values that aren't intended to be used to variables can potentially introduce subtle bugs that are difficult to catch. Normally I'd either:
SomeType variable1; //want to store something that will be out of scope later
using(blah)
{
//...
variable1=blah;
}
//use variable1 here
or assign required value immediately:
SomeType variable2 = new SomeType();
//use variable2 immediately
or (for me, more frequently nowdays)
var variable2 = new SomeType();
assigning null/placeholder values is mainly pointless.

I use var for assignment. However I always declare instances using the class. I generally also instantiate them at the time to avoid unexpected NullReferenceExceptions

The code is ok.
Just make sure that you don't copy this technique to initialize enums where 0 is not default value or flagged enumerations.
[Flags]
public enum MyFlags
{
Test = 1,
Test2 = 2
}
MyFlags flags = default(MyFlags);
Console.WriteLine(flags); // oops

What are your favorite little used C# trick? [duplicate]

As it currently stands, this question is not a good fit for our Q&A format. We expect answers to be supported by facts, references, or expertise, but this question will likely solicit debate, arguments, polling, or extended discussion. If you feel that this question can be improved and possibly reopened, visit the help center for guidance.
Closed 11 years ago.
Locked. This question and its answers are locked because the question is off-topic but has historical significance. It is not currently accepting new answers or interactions.
This came to my mind after I learned the following from this question:
where T : struct
We, C# developers, all know the basics of C#. I mean declarations, conditionals, loops, operators, etc.
Some of us even mastered the stuff like Generics, anonymous types, lambdas, LINQ, ...
But what are the most hidden features or tricks of C# that even C# fans, addicts, experts barely know?
Here are the revealed features so far:
Keywords
yield by Michael Stum
var by Michael Stum
using() statement by kokos
readonly by kokos
as by Mike Stone
as / is by Ed Swangren
as / is (improved) by Rocketpants
default by deathofrats
global:: by pzycoman
using() blocks by AlexCuse
volatile by Jakub Šturc
extern alias by Jakub Šturc
Attributes
DefaultValueAttribute by Michael Stum
ObsoleteAttribute by DannySmurf
DebuggerDisplayAttribute by Stu
DebuggerBrowsable and DebuggerStepThrough by bdukes
ThreadStaticAttribute by marxidad
FlagsAttribute by Martin Clarke
ConditionalAttribute by AndrewBurns
Syntax
?? (coalesce nulls) operator by kokos
Number flaggings by Nick Berardi
where T:new by Lars Mæhlum
Implicit generics by Keith
One-parameter lambdas by Keith
Auto properties by Keith
Namespace aliases by Keith
Verbatim string literals with # by Patrick
enum values by lfoust
#variablenames by marxidad
event operators by marxidad
Format string brackets by Portman
Property accessor accessibility modifiers by xanadont
Conditional (ternary) operator (?:) by JasonS
checked and unchecked operators by Binoj Antony
implicit and explicit operators by Flory
Language Features
Nullable types by Brad Barker
Anonymous types by Keith
__makeref __reftype __refvalue by Judah Himango
Object initializers by lomaxx
Format strings by David in Dakota
Extension Methods by marxidad
partial methods by Jon Erickson
Preprocessor directives by John Asbeck
DEBUG pre-processor directive by Robert Durgin
Operator overloading by SefBkn
Type inferrence by chakrit
Boolean operators taken to next level by Rob Gough
Pass value-type variable as interface without boxing by Roman Boiko
Programmatically determine declared variable type by Roman Boiko
Static Constructors by Chris
Easier-on-the-eyes / condensed ORM-mapping using LINQ by roosteronacid
__arglist by Zac Bowling
Visual Studio Features
Select block of text in editor by Himadri
Snippets by DannySmurf
Framework
TransactionScope by KiwiBastard
DependantTransaction by KiwiBastard
Nullable<T> by IainMH
Mutex by Diago
System.IO.Path by ageektrapped
WeakReference by Juan Manuel
Methods and Properties
String.IsNullOrEmpty() method by KiwiBastard
List.ForEach() method by KiwiBastard
BeginInvoke(), EndInvoke() methods by Will Dean
Nullable<T>.HasValue and Nullable<T>.Value properties by Rismo
GetValueOrDefault method by John Sheehan
Tips & Tricks
Nice method for event handlers by Andreas H.R. Nilsson
Uppercase comparisons by John
Access anonymous types without reflection by dp
A quick way to lazily instantiate collection properties by Will
JavaScript-like anonymous inline-functions by roosteronacid
Other
netmodules by kokos
LINQBridge by Duncan Smart
Parallel Extensions by Joel Coehoorn

This isn't C# per se, but I haven't seen anyone who really uses System.IO.Path.Combine() to the extent that they should. In fact, the whole Path class is really useful, but no one uses it!
I'm willing to bet that every production app has the following code, even though it shouldn't:
string path = dir + "\\" + fileName;

lambdas and type inference are underrated. Lambdas can have multiple statements and they double as a compatible delegate object automatically (just make sure the signature match) as in:
Console.CancelKeyPress +=
(sender, e) => {
Console.WriteLine("CTRL+C detected!\n");
e.Cancel = true;
};
Note that I don't have a new CancellationEventHandler nor do I have to specify types of sender and e, they're inferable from the event. Which is why this is less cumbersome to writing the whole delegate (blah blah) which also requires you to specify types of parameters.
Lambdas don't need to return anything and type inference is extremely powerful in context like this.
And BTW, you can always return Lambdas that make Lambdas in the functional programming sense. For example, here's a lambda that makes a lambda that handles a Button.Click event:
Func<int, int, EventHandler> makeHandler =
(dx, dy) => (sender, e) => {
var btn = (Button) sender;
btn.Top += dy;
btn.Left += dx;
};
btnUp.Click += makeHandler(0, -1);
btnDown.Click += makeHandler(0, 1);
btnLeft.Click += makeHandler(-1, 0);
btnRight.Click += makeHandler(1, 0);
Note the chaining: (dx, dy) => (sender, e) =>
Now that's why I'm happy to have taken the functional programming class :-)
Other than the pointers in C, I think it's the other fundamental thing you should learn :-)

From Rick Strahl:
You can chain the ?? operator so that you can do a bunch of null comparisons.
string result = value1 ?? value2 ?? value3 ?? String.Empty;

Aliased generics:
using ASimpleName = Dictionary<string, Dictionary<string, List<string>>>;
It allows you to use ASimpleName, instead of Dictionary<string, Dictionary<string, List<string>>>.
Use it when you would use the same generic big long complex thing in a lot of places.

From CLR via C#:
When normalizing strings, it is highly
recommended that you use
ToUpperInvariant instead of
ToLowerInvariant because Microsoft has
optimized the code for performing
uppercase comparisons.
I remember one time my coworker always changed strings to uppercase before comparing. I've always wondered why he does that because I feel it's more "natural" to convert to lowercase first. After reading the book now I know why.

My favorite trick is using the null coalesce operator and parentheses to automagically instantiate collections for me.
private IList<Foo> _foo;
public IList<Foo> ListOfFoo
{ get { return _foo ?? (_foo = new List<Foo>()); } }

Avoid checking for null event handlers
Adding an empty delegate to events at declaration, suppressing the need to always check the event for null before calling it is awesome. Example:
public delegate void MyClickHandler(object sender, string myValue);
public event MyClickHandler Click = delegate {}; // add empty delegate!
Let you do this
public void DoSomething()
{
Click(this, "foo");
}
Instead of this
public void DoSomething()
{
// Unnecessary!
MyClickHandler click = Click;
if (click != null) // Unnecessary!
{
click(this, "foo");
}
}
Please also see this related discussion and this blog post by Eric Lippert on this topic (and possible downsides).

Everything else, plus
1) implicit generics (why only on methods and not on classes?)
void GenericMethod<T>( T input ) { ... }
//Infer type, so
GenericMethod<int>(23); //You don't need the <>.
GenericMethod(23); //Is enough.
2) simple lambdas with one parameter:
x => x.ToString() //simplify so many calls
3) anonymous types and initialisers:
//Duck-typed: works with any .Add method.
var colours = new Dictionary<string, string> {
{ "red", "#ff0000" },
{ "green", "#00ff00" },
{ "blue", "#0000ff" }
};
int[] arrayOfInt = { 1, 2, 3, 4, 5 };
Another one:
4) Auto properties can have different scopes:
public int MyId { get; private set; }
Thanks #pzycoman for reminding me:
5) Namespace aliases (not that you're likely to need this particular distinction):
using web = System.Web.UI.WebControls;
using win = System.Windows.Forms;
web::Control aWebControl = new web::Control();
win::Control aFormControl = new win::Control();

I didn't know the "as" keyword for quite a while.
MyClass myObject = (MyClass) obj;
vs
MyClass myObject = obj as MyClass;
The second will return null if obj isn't a MyClass, rather than throw a class cast exception.

Two things I like are Automatic properties so you can collapse your code down even further:
private string _name;
public string Name
{
get
{
return _name;
}
set
{
_name = value;
}
}
becomes
public string Name { get; set;}
Also object initializers:
Employee emp = new Employee();
emp.Name = "John Smith";
emp.StartDate = DateTime.Now();
becomes
Employee emp = new Employee {Name="John Smith", StartDate=DateTime.Now()}

The 'default' keyword in generic types:
T t = default(T);
results in a 'null' if T is a reference type, and 0 if it is an int, false if it is a boolean,
etcetera.

Attributes in general, but most of all DebuggerDisplay. Saves you years.

The # tells the compiler to ignore any
escape characters in a string.
Just wanted to clarify this one... it doesn't tell it to ignore the escape characters, it actually tells the compiler to interpret the string as a literal.
If you have
string s = #"cat
dog
fish"
it will actually print out as (note that it even includes the whitespace used for indentation):
cat
dog
fish

I think one of the most under-appreciated and lesser-known features of C# (.NET 3.5) are Expression Trees, especially when combined with Generics and Lambdas. This is an approach to API creation that newer libraries like NInject and Moq are using.
For example, let's say that I want to register a method with an API and that API needs to get the method name
Given this class:
public class MyClass
{
public void SomeMethod() { /* Do Something */ }
}
Before, it was very common to see developers do this with strings and types (or something else largely string-based):
RegisterMethod(typeof(MyClass), "SomeMethod");
Well, that sucks because of the lack of strong-typing. What if I rename "SomeMethod"? Now, in 3.5 however, I can do this in a strongly-typed fashion:
RegisterMethod<MyClass>(cl => cl.SomeMethod());
In which the RegisterMethod class uses Expression<Action<T>> like this:
void RegisterMethod<T>(Expression<Action<T>> action) where T : class
{
var expression = (action.Body as MethodCallExpression);
if (expression != null)
{
// TODO: Register method
Console.WriteLine(expression.Method.Name);
}
}
This is one big reason that I'm in love with Lambdas and Expression Trees right now.

"yield" would come to my mind. Some of the attributes like [DefaultValue()] are also among my favorites.
The "var" keyword is a bit more known, but that you can use it in .NET 2.0 applications as well (as long as you use the .NET 3.5 compiler and set it to output 2.0 code) does not seem to be known very well.
Edit: kokos, thanks for pointing out the ?? operator, that's indeed really useful. Since it's a bit hard to google for it (as ?? is just ignored), here is the MSDN documentation page for that operator: ?? Operator (C# Reference)

I tend to find that most C# developers don't know about 'nullable' types. Basically, primitives that can have a null value.
double? num1 = null;
double num2 = num1 ?? -100;
Set a nullable double, num1, to null, then set a regular double, num2, to num1 or -100 if num1 was null.
http://msdn.microsoft.com/en-us/library/1t3y8s4s(VS.80).aspx
one more thing about Nullable type:
DateTime? tmp = new DateTime();
tmp = null;
return tmp.ToString();
it is return String.Empty. Check this link for more details

Here are some interesting hidden C# features, in the form of undocumented C# keywords:
__makeref
__reftype
__refvalue
__arglist
These are undocumented C# keywords (even Visual Studio recognizes them!) that were added to for a more efficient boxing/unboxing prior to generics. They work in coordination with the System.TypedReference struct.
There's also __arglist, which is used for variable length parameter lists.
One thing folks don't know much about is System.WeakReference -- a very useful class that keeps track of an object but still allows the garbage collector to collect it.
The most useful "hidden" feature would be the yield return keyword. It's not really hidden, but a lot of folks don't know about it. LINQ is built atop this; it allows for delay-executed queries by generating a state machine under the hood. Raymond Chen recently posted about the internal, gritty details.

Unions (the C++ shared memory kind) in pure, safe C#
Without resorting to unsafe mode and pointers, you can have class members share memory space in a class/struct. Given the following class:
[StructLayout(LayoutKind.Explicit)]
public class A
{
[FieldOffset(0)]
public byte One;
[FieldOffset(1)]
public byte Two;
[FieldOffset(2)]
public byte Three;
[FieldOffset(3)]
public byte Four;
[FieldOffset(0)]
public int Int32;
}
You can modify the values of the byte fields by manipulating the Int32 field and vice-versa. For example, this program:
static void Main(string[] args)
{
A a = new A { Int32 = int.MaxValue };
Console.WriteLine(a.Int32);
Console.WriteLine("{0:X} {1:X} {2:X} {3:X}", a.One, a.Two, a.Three, a.Four);
a.Four = 0;
a.Three = 0;
Console.WriteLine(a.Int32);
}
Outputs this:
2147483647
FF FF FF 7F
65535
just add
using System.Runtime.InteropServices;

Using # for variable names that are keywords.
var #object = new object();
var #string = "";
var #if = IpsoFacto();

If you want to exit your program without calling any finally blocks or finalizers use FailFast:
Environment.FailFast()

Returning anonymous types from a method and accessing members without reflection.
// Useful? probably not.
private void foo()
{
var user = AnonCast(GetUserTuple(), new { Name = default(string), Badges = default(int) });
Console.WriteLine("Name: {0} Badges: {1}", user.Name, user.Badges);
}
object GetUserTuple()
{
return new { Name = "dp", Badges = 5 };
}
// Using the magic of Type Inference...
static T AnonCast<T>(object obj, T t)
{
return (T) obj;
}

Here's a useful one for regular expressions and file paths:
"c:\\program files\\oldway"
#"c:\program file\newway"
The # tells the compiler to ignore any escape characters in a string.

Mixins. Basically, if you want to add a feature to several classes, but cannot use one base class for all of them, get each class to implement an interface (with no members). Then, write an extension method for the interface, i.e.
public static DeepCopy(this IPrototype p) { ... }
Of course, some clarity is sacrificed. But it works!

Not sure why anyone would ever want to use Nullable<bool> though. :-)
True, False, FileNotFound?

This one is not "hidden" so much as it is misnamed.
A lot of attention is paid to the algorithms "map", "reduce", and "filter". What most people don't realize is that .NET 3.5 added all three of these algorithms, but it gave them very SQL-ish names, based on the fact that they're part of LINQ.
"map" => Select Transforms data
from one form into another
"reduce" => Aggregate Aggregates
values into a single result
"filter" => Where Filters data
based on a criteria
The ability to use LINQ to do inline work on collections that used to take iteration and conditionals can be incredibly valuable. It's worth learning how all the LINQ extension methods can help make your code much more compact and maintainable.

Environment.NewLine
for system independent newlines.

If you're trying to use curly brackets inside a String.Format expression...
int foo = 3;
string bar = "blind mice";
String.Format("{{I am in brackets!}} {0} {1}", foo, bar);
//Outputs "{I am in brackets!} 3 blind mice"

?? - coalescing operator
using (statement / directive) - great keyword that can be used for more than just calling Dispose
readonly - should be used more
netmodules - too bad there's no support in Visual Studio

#Ed, I'm a bit reticent about posting this as it's little more than nitpicking. However, I would point out that in your code sample:
MyClass c;
if (obj is MyClass)
c = obj as MyClass
If you're going to use 'is', why follow it up with a safe cast using 'as'? If you've ascertained that obj is indeed MyClass, a bog-standard cast:
c = (MyClass)obj
...is never going to fail.
Similarly, you could just say:
MyClass c = obj as MyClass;
if(c != null)
{
...
}
I don't know enough about .NET's innards to be sure, but my instincts tell me that this would cut a maximum of two type casts operations down to a maximum of one. It's hardly likely to break the processing bank either way; personally, I think the latter form looks cleaner too.

Maybe not an advanced technique, but one I see all the time that drives me crazy:
if (x == 1)
{
x = 2;
}
else
{
x = 3;
}
can be condensed to:
x = (x==1) ? 2 : 3;

Returning a value type from a property

I'm getting confused with what happens on the stack and heap in respect to value type properties in classes.
My understanding so far:
When you create a class with a structure (value type) like this:
class Foo
{
private Bar _BarStruct;
public Bar BarStruct
{
get {return _BarStruct; }
set {_BarStruct = value; }
}
}
private struct Bar
{
public int Number;
Bar()
{
Number = 1;
}
Bar(int i)
{
Number = i;
}
}
If you create a class instance like so:
Foo fooObj = new Foo();
The stack and heap will look like this:
...where the Bar structure is embeded in the Foo class in the heap. This makes sense to me, but I start to loose it when we consider modifying the Number integer in the BarStruct class, within the Foo Object. For example:
Foo fooObj = new Foo();
fooObj.BarStruct.Number = 1;
As I understand, this should be returning a copy of BarStruct to live on the stack, which means that any changes of a member of BarStruct would not be carried through to the object, which is why the last line above gives an error.
Is this right so far?
If so, my question is, how come an assignment such as this:
fooObj.BarStruct = new Bar(2);
...is valid and changes the heap value? Surely this is just changing the value on the stack?? Also, (by and by) I find it so confusing that you are able to use new on a value type. To me, new is for allocatting on the heap (as per C++) and feels unnatural to be doing this for items on the stack.
So just to re-iterate the question, Am I correct in my assumption of what happens when a property containing a structure is called and why can you assign a new structure to a copy and yet it still changes the reference on the heap?
Really hope this all make sense.
Yell if you need clarification!
Ta,
Andy.

Looking at this assignment:
fooObj.BarStruct = new Bar(2);
The assignment isn't changing the value on the stack - it's calling the setter for the property.
In other words, whereas your first assignment is equivalent to:
fooObj.get_BarStruct().Number = 1; // Bad
the second is equivalent to:
fooObj.set_BarStruct(new Bar(2));
Does that help?
Note that the problematic assignment becomes a non-issue if you make your value type immutable to start with - which helps in general, in fact. Mutable value types are a really bad idea in C#; you can get into no end of trouble with them.
In terms of your expectations of "new" - try not to think in C++, basically. C# isn't C++, and various things (destructors, generics, behaviour during construction) will confuse you if you try to effectively write C++ in C#. A "new" statement creates a new instance of a type, whether that's a value type or a reference type.