struct ToString() not automatically invoked

[Zytan]

Everything (er, every class) in C# has ToString() which is
conveniently automatically invoked when using it in Debug.WriteLine ()
or in a string concatenation, etc. I made a struct, and I want to
make a method to print out its data in a similar format. So, I did
this:

public struct MyStruct
{
public override string ToString()
{
return ("Hello");
}
}

But, it doesn't get automatically invoked. It complains if I don't
put "public" or "override", so I assume it knows that it's overriding
something (I am not sure what, since it's not a class, and thus not an
object). So:
1. why does it complain without "override"? and
2. why isn't it automatically invoked?

I know classes are references and structs are value types. Since the
struct isn't a class, I don't even know *why* it is complaining about
my creation of a ToString() method in it. I would expect it wouldn't
complain, and also wouldn't be invoked automatically. But, since it
does complain surprisingly, I thought maybe it would also be invoked
automatically, which it doesn't.

Zytan

[Mattias Sjögren]

>1. why does it complain without "override"? and

Because a method with the same signature is defined in a base class
(System.Object in this case).

>2. why isn't it automatically invoked?

In what situation is it not invoked? The following prints "Hello
Hello" as expected for me

public struct MyStruct
{
public override string ToString()
{
return ("Hello");
}
}

class Test
{
static void Main()
{
MyStruct m = new MyStruct();
Console.WriteLi ne("Hello " + m);
}
}
Mattias

--
Mattias Sjögren [C# MVP] mattias @ mvps.org
http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com
Please reply only to the newsgroup.

[Jon Skeet [C# MVP]]

Zytan <zy**********@y ahoo.comwrote:

Everything (er, every class) in C# has ToString() which is
conveniently automatically invoked when using it in Debug.WriteLine ()
or in a string concatenation, etc. I made a struct, and I want to
make a method to print out its data in a similar format. So, I did
this:

public struct MyStruct
{
public override string ToString()
{
return ("Hello");
}
}

But, it doesn't get automatically invoked.

In what situation? Here's a test which shows it being invoked:

using System;

public struct MyStruct
{
public override string ToString()
{
return ("Hello");
}
}

class Test
{
static void Main()
{
MyStruct foo = new MyStruct();
Console.WriteLi ne (foo);
}
}

It complains if I don't
put "public" or "override", so I assume it knows that it's overriding
something (I am not sure what, since it's not a class, and thus not an
object).

It still (sort of) derives from object - you are genuinely overriding a
method here. The details are pretty fiddly.

So:
1. why does it complain without "override"? and

Because then you'd be hiding the method instead of overriding it.

2. why isn't it automatically invoked?

When are you expecting it to be automatically invoked?

I know classes are references and structs are value types. Since the
struct isn't a class, I don't even know *why* it is complaining about
my creation of a ToString() method in it. I would expect it wouldn't
complain, and also wouldn't be invoked automatically. But, since it
does complain surprisingly, I thought maybe it would also be invoked
automatically, which it doesn't.

Without more details of when you'd expect it to be invoked, it's
impossible to answer you.

Could you post a short but complete program which demonstrates the
problem?

See http://www.pobox.com/~skeet/csharp/complete.html for details of
what I mean by that.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
If replying to the group, please do not mail me too

[Bill Butler]

I don't know what you are doing wrong. It should work.

---------------------------------
using System;

class Test
{
public static void Main()
{
MyStruct x = new MyStruct();
Console.WriteLi ne("{0}", x);
}
}

public struct MyStruct
{
public override string ToString()
{
return ("Hello");
}
}

-----------------------------------
This definitely prints "Hello"

"Zytan" <zy**********@y ahoo.comwrote in message
news:11******** *************@j 27g2000cwj.goog legroups.com...

Everything (er, every class) in C# has ToString() which is
conveniently automatically invoked when using it in Debug.WriteLine ()
or in a string concatenation, etc. I made a struct, and I want to
make a method to print out its data in a similar format. So, I did
this:

public struct MyStruct
{
public override string ToString()
{
return ("Hello");
}
}

But, it doesn't get automatically invoked. It complains if I don't
put "public" or "override", so I assume it knows that it's overriding
something (I am not sure what, since it's not a class, and thus not an
object). So:
1. why does it complain without "override"? and
2. why isn't it automatically invoked?

I know classes are references and structs are value types. Since the
struct isn't a class, I don't even know *why* it is complaining about
my creation of a ToString() method in it. I would expect it wouldn't
complain, and also wouldn't be invoked automatically. But, since it
does complain surprisingly, I thought maybe it would also be invoked
automatically, which it doesn't.

Zytan

[Zytan]

Ok, you guys rock, thanks for posting the code samples. Jon, I've
created a 'complete' program that shows the error (and yes, it
certainly helps to narrow down exactly what is wrong, and most often
shows the err in your ways). The problem occurs when I have my *own
function* that accepts a string. In this case, the conversion from
struct to string does not implicitly take place.

class Program
{
public struct MyStruct
{
public int x;
public override string ToString()
{
return "Hello!";
}
}
static void Main(string[] args)
{
MyStruct s;
s.x = 5;
Print(s); // doesn't compile
Print(s.ToStrin g()); // compiles
}
static void Print(string s)
{
Console.WriteLi ne(s);
}
}

Zytan

[Zytan]

1. why does it complain without "override"? and

>
Because a method with the same signature is defined in a base class
(System.Object in this case).

Ok, so, structs DO derive from object. Strange. I guess the evidence
suggest that, doesn't it?

2. why isn't it automatically invoked?

In what situation is it not invoked?

Please see my program in another post in this thread.

Thanks, Mattias

Zytan

[Zytan]

But, it doesn't get automatically invoked.

>
In what situation?

Please see my program in another post.

It complains if I don't
put "public" or "override", so I assume it knows that it's overriding
something (I am not sure what, since it's not a class, and thus not an
object).

It still (sort of) derives from object - you are genuinely overriding a
method here. The details are pretty fiddly.

Ah.

So:
1. why does it complain without "override"? and

Because then you'd be hiding the method instead of overriding it.

Yes, of course. Now that I know it's derived from object, it makes
sense.

2. why isn't it automatically invoked?

When are you expecting it to be automatically invoked?

It's when I pass it to my own function that accepts a string
parameter.
Please see the program in another post.

Thanks, Jon

Zytan

[Zytan]

I don't know what you are doing wrong. It should work.

I don't think I am doing anything wrong. Call your own function that
takes a string instead of Console.WriteLi ne in your program, and
you'll see that it doesn't work.

Please see my program in another post.

Thanks, Bill.

Zytan

[Jon Skeet [C# MVP]]

Zytan <zy**********@y ahoo.comwrote:

Ok, you guys rock, thanks for posting the code samples. Jon, I've
created a 'complete' program that shows the error (and yes, it
certainly helps to narrow down exactly what is wrong, and most often
shows the err in your ways). The problem occurs when I have my *own
function* that accepts a string. In this case, the conversion from
struct to string does not implicitly take place.

No, it doesn't - and it doesn't for classes either, thankfully. Why did
you expect that it would?

You could add your own implicit conversion to a string, although I
wouldn't recommend it.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
If replying to the group, please do not mail me too

[Bill Butler]

"Zytan" <zy**********@y ahoo.comwrote in message
news:11******** **************@ 64g2000cwx.goog legroups.com...

>I don't know what you are doing wrong. It should work.

I don't think I am doing anything wrong. Call your own function that
takes a string instead of Console.WriteLi ne in your program, and
you'll see that it doesn't work.

You could overload your Print method a few times to get the behavior
that you desire

for instance, this would work.

static void Print(object obj)
{
Console.WriteLi ne(obj);
}
You could make your Print method accept formatting strings as well if
you write those overloads

Good luck
Bill