meta-generics

[Wiktor Zychla [C# MVP]]

suppose I have a class

class MyContainter {
List<something1 list1;
List<something2 list2;
...
List<somethingn listn;

othertype1 otherfield1;
...
othertypek otherfieldk;
}

as you can see there are plenty of generics instantiated with different
types.

what I wish is to use reflection to get a list of fields that are of type
List<anything>:

foreach ( FieldInfo fi in typeof(MyContai nter).GetFields () )
{
object val = fi.GetValue( TheInstance );

if ( ???? )
{
}
}

what is the best approach to fill the ???? gap so that I have only all these
List<Tfields passed into the if block?

solutions I think about are:
a) matching the type by name - however this is ugly
b) additional attribute on all List<Tfields - seems unnecessary

what I would like is to use pure reflection. something like:

if ( val is List ) { }
if ( val.GetType().I sSubclassOf( ... ) ) { }

however, none of my tries compile since List<is a generic type and cannot
be used without instantiation of the generic argument. in other words, I
cannot make generics generic on another level of abstraction.

is it possible at all? right now I tend to think that this is impossible.

[I should mention that in the real-life application there are no List<T>
fields but my_own_generic_ class<T,Kso any List<Tspecific solutions are
not acceptable]

Thanks in advance,
Wiktor Zychla

[Barry Kelly]

"Wiktor Zychla [C# MVP]" <wz*****@nospm. ii.uni.wroc.pl. nospmwrote:

class MyContainter {
List<something1 list1;

what I wish is to use reflection to get a list of fields that are of type
List<anything>:

foreach ( FieldInfo fi in typeof(MyContai nter).GetFields () )
{

Type t = fi.FieldType;

if (t.IsGenericTyp e
&& t.GetGenericTyp eDefinition() == typeof(List<>)
&& t.GetGenericArg uments()[0] == typeof(anything ))
// ...

-- Barry

--
http://barrkel.blogspot.com/

[Barry Kelly]

Barry Kelly <ba***********@ gmail.comwrote:

"Wiktor Zychla [C# MVP]" <wz*****@nospm. ii.uni.wroc.pl. nospmwrote:

class MyContainter {
List<something1 list1;

what I wish is to use reflection to get a list of fields that are of type
List<anything>:

foreach ( FieldInfo fi in typeof(MyContai nter).GetFields () )
{

Type t = fi.FieldType;

if (t.IsGenericTyp e
&& t.GetGenericTyp eDefinition() == typeof(List<>)
&& t.GetGenericArg uments()[0] == typeof(anything ))
// ...

I should point out that this is most suitable if you don't already know
that you're dealing with 'anything'. If you do statically know the type,
then you can simply do:

if (fi.FieldType == typeof(List<any thing>))

-- Barry

--
http://barrkel.blogspot.com/

[Greg Young]

I am not sure I follow the question.

You have an instance (so you would be dealing with the closed type of the
generic from getvalue)

could you use Type.GetGeneric TypeDefinition( ) to get the open version of the
generic type.then compare this to the type you are after?

If I am understanding you correctly something like this??
public class Foo<T{
public List<Tbar;
public List<Tbar2;
public int test;
public float test2;
public Foo() {
bar = new List<T>();
bar2 = new List<T>();
}

}

static void CheckForFieldTy pe(object o, Type ToFind) {
foreach (FieldInfo fi in o.GetType().Get Fields()) {
if (fi.FieldType.I sGenericType &&
fi.FieldType.Ge tGenericTypeDef inition() == ToFind) {
Console.WriteLi ne("Found " + fi.Name);
}
}
}

static void Main(string[] args) {
Foo<intfoo = new Foo<int>();
CheckForFieldTy pe(foo, typeof(List<>)) ;
}
Cheers,

Greg Young
MVP - C#
http://codebetter.com/blogs/gregyoung

"Wiktor Zychla [C# MVP]" <wz*****@nospm. ii.uni.wroc.pl. nospmwrote in
message news:Oa******** *****@TK2MSFTNG P05.phx.gbl...

suppose I have a class

class MyContainter {
List<something1 list1;
List<something2 list2;
...
List<somethingn listn;

othertype1 otherfield1;
...
othertypek otherfieldk;
}

as you can see there are plenty of generics instantiated with different
types.

what I wish is to use reflection to get a list of fields that are of type
List<anything>:

foreach ( FieldInfo fi in typeof(MyContai nter).GetFields () )
{
object val = fi.GetValue( TheInstance );

if ( ???? )
{
}
}

what is the best approach to fill the ???? gap so that I have only all
these List<Tfields passed into the if block?

solutions I think about are:
a) matching the type by name - however this is ugly
b) additional attribute on all List<Tfields - seems unnecessary

what I would like is to use pure reflection. something like:

if ( val is List ) { }
if ( val.GetType().I sSubclassOf( ... ) ) { }

however, none of my tries compile since List<is a generic type and
cannot be used without instantiation of the generic argument. in other
words, I cannot make generics generic on another level of abstraction.

is it possible at all? right now I tend to think that this is impossible.

[I should mention that in the real-life application there are no List<T>
fields but my_own_generic_ class<T,Kso any List<Tspecific solutions are
not acceptable]

Thanks in advance,
Wiktor Zychla

[Greg Young]

too quick for me .. :( was typing up that quick example

Cheers,

Greg
"Barry Kelly" <ba***********@ gmail.comwrote in message
news:or******** *************** *********@4ax.c om...

Barry Kelly <ba***********@ gmail.comwrote:

>"Wiktor Zychla [C# MVP]" <wz*****@nospm. ii.uni.wroc.pl. nospmwrote:

class MyContainter {
List<something1 list1;

what I wish is to use reflection to get a list of fields that are of
type
List<anything>:

foreach ( FieldInfo fi in typeof(MyContai nter).GetFields () )
{

Type t = fi.FieldType;

if (t.IsGenericTyp e
&& t.GetGenericTyp eDefinition() == typeof(List<>)
&& t.GetGenericArg uments()[0] == typeof(anything ))
// ...

I should point out that this is most suitable if you don't already know
that you're dealing with 'anything'. If you do statically know the type,
then you can simply do:

if (fi.FieldType == typeof(List<any thing>))

-- Barry

--
http://barrkel.blogspot.com/

[Wiktor Zychla [C# MVP]]

too quick for me .. :( was typing up that quick example

big thanks for both of you. what I missed is the possibility of having an
"open" generic type with:

typeof( generictype<)

this solves my problem completely.

regards,
Wiktor