Why is class Sample<T> where T : Stream, class ILLEGAL

[puzzlecracker]

Would someone explain why this declaration is illegal: class Sample<T>
where T : Stream, class

[puzzlecracker]

Re: Why is class Sample&lt;T&gt; where T : Stream, class ILLEGAL

On Nov 3, 1:54 pm, puzzlecracker <ironsel2...@gm ail.comwrote:

Would someone explain why this declaration is illegal: class Sample<T>
where T : Stream, class

They are taken from C# In depth book
And a few more that are also illegal, and I don't understand why
(compiler is less than helpful).

class Sample<Twhere T : Stream, class

class Sample<Twhere T : new(), Stream

class Sample<T,Uwhere T : struct where U : class, T

class Sample<T,Uwhere T : Stream, U : IDisposable

[Ashutosh Bhawasinka]

Re: Why is class Sample&lt;T&gt; where T : Stream, class ILLEGAL

You can restrict the generic implementation by either a base type or
value/reference type. Not both.

Stream is already a class. So, T will be a reference type (class) if you
restrict T to be a Stream. So, basically you are trying to say class 2
times.


puzzlecracker wrote:

Would someone explain why this declaration is illegal: class Sample<T>
where T : Stream, class
>

[Stanimir Stoyanov]

Re: Why is class Sample&lt;T&gt; where T : Stream, class ILLEGAL

Any 'class' or 'struct' constraints should come first but why are you adding
an 'all classes' constraints if you would like to use this generic class
with Stream and derivative classes?
--
Stanimir Stoyanov

http://stoyanoff.info

"puzzlecrac ker" <ironsel2000@gm ail.comwrote in message
news:453a59ab-d472-43ae-98b2-9a96ee71b0a5@z6 g2000pre.google groups.com...

Would someone explain why this declaration is illegal: class Sample<T>
where T : Stream, class

[Ashutosh Bhawasinka]

Re: Why is class Sample&lt;T&gt; where T : Stream, class ILLEGAL

Also, restriction by value/reference type has to be the first
constraint. And restriction of new has to be the last.

In this case you will get the error saying that it should be the first
constraint (similar message). If you change it to

class Sample<T>
where T : class,Stream

then my previous comment applies.

puzzlecracker wrote:

Would someone explain why this declaration is illegal: class Sample<T>
where T : Stream, class
>

[Peter Duniho]

Re: Why is class Sample&lt;T&gt; where T : Stream, class ILLEGAL

On Mon, 03 Nov 2008 10:54:57 -0800, puzzlecracker <ironsel2000@gm ail.com>
wrote:

Would someone explain why this declaration is illegal: class Sample<T>
where T : Stream, class

Well, what does the error message say?

Here's a hint: what kind of type is "Stream"? Is there _any_ type you
could use with the "class" constraint that would either not be redundant
or contradictory?

[Ashutosh Bhawasinka]

Re: Why is class Sample&lt;T&gt; where T : Stream, class ILLEGAL

new()
has to be the last constraint!

for multiple generic type you need to have the where clause for each
generic type. Like this

class Sample<T, Uwhere T: Stream where U:IDisposable


puzzlecracker wrote:

On Nov 3, 1:54 pm, puzzlecracker <ironsel2...@gm ail.comwrote:
>

>Would someone explain why this declaration is illegal: class Sample<T>
>where T : Stream, class
>>

>
They are taken from C# In depth book
And a few more that are also illegal, and I don't understand why
(compiler is less than helpful).
>
class Sample<Twhere T : Stream, class
>
class Sample<Twhere T : new(), Stream
>
class Sample<T,Uwhere T : struct where U : class, T
>
class Sample<T,Uwhere T : Stream, U : IDisposable
>

[puzzlecracker]

Re: Why is class Sample&lt;T&gt; where T : Stream, class ILLEGAL

On Nov 3, 2:05 pm, Ashutosh Bhawasinka <discuss...@ash utosh.inwrote:

You can restrict the generic implementation by either a base type or
value/reference type. Not both.
>
Stream is already a class. So, T will be a reference type (class) if you
restrict T to be a Stream. So, basically you are trying to say class 2
times.
>
puzzlecracker wrote:

Would someone explain why this declaration is illegal: class Sample<T>
where T : Stream, class

that implies that struct, value types, cannot inherit from Reference
type... argh

[Peter Duniho]

Re: Why is class Sample&lt;T&gt; where T : Stream, class ILLEGAL

On Mon, 03 Nov 2008 11:17:05 -0800, puzzlecracker <ironsel2000@gm ail.com>
wrote:

that implies that struct, value types, cannot inherit from Reference
type... argh

Well, sort of. Value types can and do inherit reference types. For
example, enumeration types inherit Enum, and all value types inherit
Object.

But yes...no matter what specific type you call out in the constraint,
adding "class" to the constraint will either be redundant (if that type is
a reference type) or contradictory (if that type is a value type).

Pete

[Ashutosh Bhawasinka]

Re: Why is class Sample&lt;T&gt; where T : Stream, class ILLEGAL

Yes, value types (struct) can't inherit from either struct or class.
However they can (only) implement interfaces.

puzzlecracker wrote:

On Nov 3, 2:05 pm, Ashutosh Bhawasinka <discuss...@ash utosh.inwrote:
>

>You can restrict the generic implementation by either a base type or
>value/reference type. Not both.
>>
>Stream is already a class. So, T will be a reference type (class) if you
>restrict T to be a Stream. So, basically you are trying to say class 2
>times.
>>
>puzzlecracke r wrote:
>>

>>Would someone explain why this declaration is illegal: class Sample<T>
>>where T : Stream, class
>>>

>
that implies that struct, value types, cannot inherit from Reference
type... argh
>

[Ashutosh Bhawasinka]

Re: Why is class Sample&lt;T&gt; where T : Stream, class ILLEGAL

Value type does *inherit *implicitly. But no *explicit *inheritance is
allowed.

Peter Duniho wrote:

On Mon, 03 Nov 2008 11:17:05 -0800, puzzlecracker
<ironsel2000@gm ail.comwrote:
>

>that implies that struct, value types, cannot inherit from Reference
>type... argh

>
Well, sort of. Value types can and do inherit reference types. For
example, enumeration types inherit Enum, and all value types inherit
Object.
>
But yes...no matter what specific type you call out in the constraint,
adding "class" to the constraint will either be redundant (if that
type is a reference type) or contradictory (if that type is a value
type).
>
Pete

[Jon Skeet [C# MVP]]

Re: Why is class Sample&lt;T&gt; where T : Stream, class ILLEGAL

On Nov 3, 7:02 pm, puzzlecracker <ironsel2...@gm ail.comwrote:

Would someone explain why this declaration is illegal: class Sample<T>
where T : Stream, class

>
They are taken from C#  In depth book
And a few more that are also illegal, and I don't understand why
(compiler is less than helpful).

<snip>

There have been lots of good answers - but I'd just like to point out
one problem with this section of the book. There is a genuine
technical error - see http://csharpindepth.com/ViewNote.aspx?NoteID=121
for details. Basically the constraint "class Sample<Twhere T :
class, Stream, new()" is listed as valid, but it isn't.

Jon

[puzzlecracker]

Re: Why is class Sample&lt;T&gt; where T : Stream, class ILLEGAL

On Nov 4, 4:29 am, "Jon Skeet [C# MVP]" <sk...@pobox.co mwrote:

There have been lots of good answers - but I'd just like to point out
one problem with this section of the book. There is a genuine
technical error - seehttp://csharpindepth.c om/ViewNote.aspx?N oteID=121
for details. Basically the constraint "class Sample<Twhere T :
class, Stream, new()" is listed as valid, but it isn't.
>
Jon

Why would it be invalid? All it's saying that the close type of
instance is required to be class, inherit from Stream and have
parameterless constructor.

Thanks

[Marc Gravell]

Re: Why is class Sample&lt;T&gt; where T : Stream, class ILLEGAL

You are only allows one primary constraint; both ": class" and ":
Stream" are classed as primary constraints. If you think about it, this
is logical: Stream is a class, so if T : Stream, T *must* be a class.

Marc

[Jon Skeet [C# MVP]]

Re: Why is class Sample&lt;T&gt; where T : Stream, class ILLEGAL

On Nov 4, 1:53 pm, puzzlecracker <ironsel2...@gm ail.comwrote:

There have been lots of good answers - but I'd just like to point out
one problem with this section of the book. There is a genuine
technical error - see http://csharpindepth.com/ViewNote.aspx?NoteID=121
for details. Basically the constraint "class Sample<Twhere T :
class, Stream, new()" is listed as valid, but it isn't.

>
 Why would it be invalid?  All it's saying that the close type of
instance is required to be class, inherit from Stream and have
parameterless constructor.

Did you follow the link? I thought the note was pretty clear...

Jon