use of struct

[Mark Broadbent]

Is it only really a good idea to use a struct when all the struct data
contains value types? I was writing one which used and exposed a public
string array property but there are a couple of things with this.

i. I am guessing the string array held within the struct would still be
stored in the heap anyway.
ii. I have noticed that the struct must be initialised using the
constructor to set the public values since if I simply declare and set
each property seperatly, the compiler complains that the struct is
uninitialised.

e.g.
Page p; //Page is a simple struct
string[] s = {"one", "two", "three"};
p.ID = 1; // compiler states p is unassigned
p.Attributes = s;

I cannot see the point to struct in this instance where public reference
types are used since the struct is less flexible. The following compiles..

string[] s = {"one", "two", "three"};
Page p = new Page(1, s);

p.ID = 1; // I can now set the properties without compiler problem
p.Attributes = s;

What do you all think?

Br,

Mark.

[cody]

Re: use of struct

if you have struct

S
{
public int P;
public void Foo(){}
}

you can do

S s;
s.P = 1234;
s.Foo();

but you cannot do

S s;
s.Foo();
s.P = 1234;

That is because P is not a property but a field and the compiler so can
recognize when all fields are initialized and access to a method/property of
a struct is only allowed if every field is guaranteed to be initialized.
[color=blue]
> i. I am guessing the string array held within the struct would still be
> stored in the heap anyway.[/color]

Yes, it is. And storing a struct in an object would store the whole struct
in the heap.

[Mark Broadbent]

Re: use of struct

You would still have the same behaviour (in your code) if P was a
property (for the value type) -and that is fine (I am happy with that)
*but* if you tried to use a property to access a reference type the
compiler would not like that.

e.g.

//this is ok.

public struct S
{
int p;
public int P
{get {return p;}
set {p = value;}}
public void Foo(){}
}

S s;
s.P = 1234;
Foo();

//this throws compiler unassigned error;

public struct S
{
int p;
string s;
public int P
{get {return p;}
set {p = value;}}
public int S
{get {return s;}
set {s = value;}}
public void Foo(){}
}

S s;
s.P = 1234;
s.S = "Doesnt work"; //this code should compile since all values of
struct have been set
Foo();


p.s.
Value types are by default initialised to 0 in structs (if they haven't
been set thru constructor).


cody wrote:[color=blue]
> if you have struct
>
> S
> {
> public int P;
> public void Foo(){}
> }
>
> you can do
>
> S s;
> s.P = 1234;
> s.Foo();
>
> but you cannot do
>
> S s;
> s.Foo();
> s.P = 1234;
>
> That is because P is not a property but a field and the compiler so can
> recognize when all fields are initialized and access to a method/property of
> a struct is only allowed if every field is guaranteed to be initialized.
>
>[color=green]
>>i. I am guessing the string array held within the struct would still be
>>stored in the heap anyway.[/color]
>
>
> Yes, it is. And storing a struct in an object would store the whole struct
> in the heap.
>
>[/color]

[cody]

Re: use of struct

> You would still have the same behaviour (in your code) if P was a[color=blue]
> property (for the value type) -and that is fine (I am happy with that)
> *but* if you tried to use a property to access a reference type the
> compiler would not like that.
>
> e.g.
>
> //this is ok.
>
> public struct S
> {
> int p;
> public int P
> {get {return p;}
> set {p = value;}}
> public void Foo(){}
> }
>
> S s;
> s.P = 1234;
> Foo();
>
> //this throws compiler unassigned error;
>
> public struct S
> {
> int p;
> string s;
> public int P
> {get {return p;}
> set {p = value;}}
> public int S
> {get {return s;}
> set {s = value;}}
> public void Foo(){}
> }
>
> S s;
> s.P = 1234;
> s.S = "Doesnt work"; //this code should compile since all values of
> struct have been set
> Foo();
>
>
> p.s.
> Value types are by default initialised to 0 in structs (if they haven't
> been set thru constructor).[/color]

This is very strange. What could be the reason of that?