This question already has answers here:
How can I set the value of auto property backing fields in a struct constructor?
(2 answers)
Closed 9 years ago.
Using this code:
struct Foo<T1>
{
public T1 Item1 { get; private set; }
public Foo(T1 item1)
{
Item1 = item1;
}
}
I encounter this error:
Backing field for automatically implemented property 'Foo.Item1' must be fully assigned before control is returned to the caller. Consider calling the default constructor from a constructor initializer.
My question is, why is the property Item1 not fully assigned after the constructor is called?
Edit: Changed set to private set because this question has nothing to do with mutability.
Add this() in here:
public Foo(T1 item1) : this()
{
Item1 = item1;
}
It's because you're assigning to a property, and the compiler can't deduce that the property only assigns a value to a variable; it could do other things before the instance is initialized, and that's not allowed because the structure might have garbage data. So you have to initialize it with the default constructor first, then do what you want.
Related
This question already has answers here:
What is the difference between a field and a property?
(33 answers)
How to implement a read only property
(8 answers)
Closed 5 years ago.
Yes, I've googled the question but the answers I've found only refer to the old days, before there were getter-only auto-properties.
Today in C# you can declare this:
class Test
{
readonly int MyField;
int MyProperty { get; }
public Test()
{
MyField = 42;
MyProperty = 47;
}
}
Both declarations can only be initialized either at the line of declaration or in the constructor as seen above.
Is there still a relevant difference between those? Is one to be preferred over the other (e.g. in certain situations, except for interface declaration)?
This question already has answers here:
Why can't I initialize my fields in my structs?
(4 answers)
Closed 8 years ago.
What is the cause of the error on the screen?
public struct YetkiYapisiListesi
{
public bool STOKGUNCELLE =false ;
public bool STOKSIL=false;
public bool STOKLISTELE=false;
}
Non-static struct member cannot have initializer
C# does not allow structs to have initializers, the reason why has been debated before, see here: ( Why can't I initialize my fields in my structs? )
Simply remove the = false part from your field declarations.
Note that Boolean fields are false by default, making your assignment completely unnecessary.
If you absolutely need fields to have initialized to non-default values then you can still define an additional constructor that sets those values, however it cannot be the default (parameterless) constructor. One alternative option then, is to use a static factory method.
You can't initialize field on Struct.
You will get the same result even if you ommit initializing :
public bool STOKGUNCELLE;
public bool STOKSIL;
public bool STOKLISTELE;
public bool STOKHAREKET;
Because bool default value are false .
This question already has answers here:
What is the difference between a field and a property?
(33 answers)
Closed 9 years ago.
I have read msdn article about properties. They show that example of property:
// Declare a Name property of type string:
public string Name
{
get
{
return myName;
}
set
{
myName = value;
}
}
Then they say:
Once the properties are declared, they can be used as if they were
fields of the class.
What would be the difference if they just left:
public string Name;
If I had a field: private string name and wanted to have only getter? Should I declare
public string GetName(){return name;} or should use those properties somehow?
Could somebody tell me what is wrong with that example:
private int age;
public void setAge(int age){
if(age < 100)
this.age = age;
}
This from Clr Via C#
Field A data variable that is part of the object’s state. Fields are identified by their name and type.
Property To the caller, this member looks like a field. But to the type implementer, it looks like a method (or two). Properties allow an implementer to validate input parameters and object state before accessing the value and/or calculating a value only when necessary.
They also allow a user of the type to have simplified syntax. Finally, properties allow you to create read-only or write-only “fields."
This question already has answers here:
Any reason to use auto-implemented properties over manual implemented properties?
(7 answers)
Closed 9 years ago.
What is more "true": use properties with or without private fields.
I.e.
1.
class A
{
int _field;
public int Field
{
get{ return _field;}
set{_field = value;}
}
}
2.
class A
{
public int Field{get;private set;}
}
Number 2 creates a backing field automatically, so you always have a private field "behind the scenes" (although not directly accessible in the latter case).
when you create anonymous property compiler creates corresponding field for you, so it's pretty much the same, but you can access autocreated field only via property
It makes no difference - the compiler generates the property implementation for you in exactly the same way that it generates a default constructor or the code for a using statement. These two classes are nearly 100% equivalent which you can see if you decompile an auto-property (the only difference is the name of the generated backing field that the compiler uses)
class A
{
public int Field {get; private set;}
}
class A
{
int _field;
public int Field
{
get { return _field; }
private set {_field = value; }
}
}
Its completely down to your personal preference.
As has already been stated, the second creates the backing field at compile time. You would typically define a backing field your self if you wanted the property to act as a public accessor to the field, where you can add custom logic or prevent the value being modified (using the private keyword on the setter).
This question already has answers here:
Struct constructor: "fields must be fully assigned before control is returned to the caller."
(5 answers)
Auto-properties and structs
(3 answers)
Closed 9 years ago.
The following code suggests I cannot use implicit properties with a struct:
public struct LimitfailureRecord
{
public LimitfailureRecord(string sampleCode)
{
SampleCode = sampleCode;
}
public string SampleCode {get; set;}
{
}
}
It fails to compile, with the error message
"Backing field for automatically implemented property
'blahblah.LimitfailureRecord.SampleCode'
must be fully assigned before control is returned to the caller.
Consider calling the default constructor from a constructor
initializer."
If I change the struct to a class it's fine.
What do I need to do to make this work as a struct? I'd rather not go to the lengths of backing fields (this is a heavily stripped down version of the real code) if I can avoid it.
With structs you have to call the default constructor in all other constructors:
public LimitfailureRecord(string sampleCode) : this()
{
SampleCode = sampleCode;
}
Use a constructor chaining like so:
public LimitfailureRecord(string sampleCode)
: this()
{
...
}
The reason is the auto-implemented property introduces a (generated) instance field for backing, as described. All instance fields must be assigned to in an instance constructor of a struct.
Actually the error text you quote describes the fix pretty well.
Something else: If you keep the set accessor of your property public you will have a mutable struct. Most people agree that mutable structs should be avoided and are "evil" because their copy-by-value semantics and the possibility of mutating an existing struct value (as in record.SampleCode = "Here's a new string for an old object";) don't go well together. Check the threads on mutable and immutable structs.
You either need to call the default constructor or change the method name.
So;
public struct LimitfailureRecord
{
public void init(string sampleCode)
{
SampleCode = sampleCode;
}
public string SampleCode { get; set; }
}
Will work or just make the method definition; LimitfailureRecord(string sampleCode) : this()
The later is better because it only requires one call to make things work. If you go the init route you have do do new LimiFfailureRecord then call init after. structs in C# simply require you to call the default constructor, this isn't the case with classes which is why it will compile if you change it to a class.