How to make derived interface property read-only ?

[Oleg Subachev]

I have one interface "Intf1" with read-write property "Prop" (with "get" and
"set" accessors).

Then I declare derived interface "Intf2" with the same property "Prop"
declared as read-only (without "set" accessor).
Property "Prop" in derived interface "Intf2" is marked with "new" modifier.

Then I implement derived interface "Intf2" in class "Clss2" with read-only
property "Prop" (without "set" accessor).
Property "Prop" in class "Clss2" is marked with "new" modifier.

During compilation I get the following error:

*******************
Clss2 does not implement interface member 'Intf1.Prop.set'
*******************

but property "Prop" is declared in interface "Intf2" and is read-only.

What's wrong ?
Oleg Subachev

[Brian Gideon]

Oleg,

Since Intf2 inherits Intf1 then Clss2 must implement everything in
Intf1 and Intf2. Now, because you've hidden a member declaration in
Intf2 using the 'new' keyword here's what you'll see happen.

Clss2 foo = new Clss2();
foo.Prop = 5; // ok

Intf1 foo = new Clss2();
foo.Prop = 5; // ok

Intf2 foo = new Clss2();
foo.Prop = 5; // compile error

Brian

Oleg Subachev wrote:

I have one interface "Intf1" with read-write property "Prop" (with "get" and
"set" accessors).

Then I declare derived interface "Intf2" with the same property "Prop"
declared as read-only (without "set" accessor).
Property "Prop" in derived interface "Intf2" is marked with "new" modifier.

Then I implement derived interface "Intf2" in class "Clss2" with read-only
property "Prop" (without "set" accessor).
Property "Prop" in class "Clss2" is marked with "new" modifier.

During compilation I get the following error:

*******************
Clss2 does not implement interface member 'Intf1.Prop.set'
*******************

but property "Prop" is declared in interface "Intf2" and is read-only.

What's wrong ?
Oleg Subachev

[Jon Skeet [C# MVP]]

Oleg Subachev <ol**@urvb.ruwrote:

I have one interface "Intf1" with read-write property "Prop" (with "get" and
"set" accessors).

Then I declare derived interface "Intf2" with the same property "Prop"
declared as read-only (without "set" accessor).
Property "Prop" in derived interface "Intf2" is marked with "new" modifier.

Then I implement derived interface "Intf2" in class "Clss2" with read-only
property "Prop" (without "set" accessor).
Property "Prop" in class "Clss2" is marked with "new" modifier.

During compilation I get the following error:

*******************
Clss2 does not implement interface member 'Intf1.Prop.set'
*******************

but property "Prop" is declared in interface "Intf2" and is read-only.

What's wrong ?

Well, you've declared that the class implements the first interface
(because the second interface derives from the first). The first
interface has a setter, therefore to implement the interface fully you
need a setter.

You can't use inheritance to "remove" members from an interface.

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
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