About Array and IList


T

Tony Johansson

Hello!

The Array class implements these interfaces IClonable, IList, ICollection
and IEnumerable.
Note only interfaces are inherited and no classes so these interfaces will
be implemented in the derived class.

In Interface IList have a couple of members that is not available from the
Array object.
For example if I do the following
int[] vector = new int[5];
And then use the intellisense on instance vector I can't see for example
Add, Remove RemoveAt
there are more but these are just example of members that are not available
from the vector instance.

So my question is how is this possible?
I must have missed something here about implementing interfaces !
I have always thought that all implemented members must be accessible from
the derived class which
is not the case in this example.

//Tony
 
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G

Göran Andersson

Tony said:
Hello!

The Array class implements these interfaces IClonable, IList, ICollection
and IEnumerable.
Note only interfaces are inherited and no classes so these interfaces will
be implemented in the derived class.

In Interface IList have a couple of members that is not available from the
Array object.
For example if I do the following
int[] vector = new int[5];
And then use the intellisense on instance vector I can't see for example
Add, Remove RemoveAt
there are more but these are just example of members that are not available
from the vector instance.

So my question is how is this possible?
I must have missed something here about implementing interfaces !
I have always thought that all implemented members must be accessible from
the derived class which
is not the case in this example.

//Tony

They are accessible from the class, but they are implemented explicitly,
which means that you need an IList reference to access them.

This compiles:

((IList)someArray).Add(42);

Of course it throws a NotSupportedException if you try to run the code.
 
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M

Martin Honnen

Tony said:
Hello!

The Array class implements these interfaces IClonable, IList, ICollection
and IEnumerable.
Note only interfaces are inherited and no classes so these interfaces will
be implemented in the derived class.

In Interface IList have a couple of members that is not available from the
Array object.
For example if I do the following
int[] vector = new int[5];
And then use the intellisense on instance vector I can't see for example
Add, Remove RemoveAt
there are more but these are just example of members that are not available
from the vector instance.

So my question is how is this possible?

You need to cast your Array to IList first:

string[] strings = new string[] { "foo", "bar" };
IList stringList = (IList)strings;
Console.WriteLine(stringList.Contains("foo"));

That is because IList is explicitly implemented by Array.
 

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