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  • Why does C# allow abstract class with no abstract members?

    - by fatcat1111
    The C# spec, section 10.1.1.1, states: An abstract class is permitted (but not required) to contain abstract members. This allows me to create classes like this: public abstract class A { public void Main() { // it's full of logic! } } This is really a concrete class; it's only abstract in so far as one can't instantiate it. If inheritors don't actually have to provide implementation, then why call it abstract?

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  • what if i keep my class members are public?

    - by anish
    In c++ instance variables are private by default,in Python variables are public by default i have two questions regarding the same:- 1: why Python have all the members are public by default? 2: People say you should your member data should be private what if i make my data to be public? what are the disadvantages of this approch? why it is a bad design?

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  • Is there a C# equivalent of typeof for properties/methods/members?

    - by David
    A classes Type metadata can be obtained in several ways. Two of them are: var typeInfo = Type.GetType("MyClass") and var typeInfo = typeof(MyClass) The advantage of the second way is that typos will be caught by the compiler, and the IDE can understand what I'm talking about (allowing features like refactoring to work without silently breaking the code) Does there exist an equivalent way of strongly referencing members/properties/methods for metadata and reflection? Can I replace: var propertyInfo = typeof(MyClass).GetProperty("MyProperty") with something like: var propertyInfo = property(MyClass.MyProperty)

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  • How do I update the members of a MySQL SET Type?

    - by MachinationX
    I have a table of values, with one of the columns being of type SET. If it currently has the members ('a', 'b', 'c', 'd'), how do I add 'e' to the possible values? I realize that using a SET type is a little strange, and I'm unclear why one would use it instead of a foreign key to another table with the values of the set, but I didn't design the database in question, and can't change it that much. Thanks for your help!

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  • What's the best way to create a static utility class in python? Is using metaclasses code smell?

    - by rsimp
    Ok so I need to create a bunch of utility classes in python. Normally I would just use a simple module for this but I need to be able to inherit in order to share common code between them. The common code needs to reference the state of the module using it so simple imports wouldn't work well. I don't like singletons, and classes that use the classmethod decorator do not have proper support for python properties. One pattern I see used a lot is creating an internal python class prefixed with an underscore and creating a single instance which is then explicitly imported or set as the module itself. This is also used by fabric to create a common environment object (fabric.api.env). I've realized another way to accomplish this would be with metaclasses. For example: #util.py class MetaFooBase(type): @property def file_path(cls): raise NotImplementedError def inherited_method(cls): print cls.file_path #foo.py from util import * import env class MetaFoo(MetaFooBase): @property def file_path(cls): return env.base_path + "relative/path" def another_class_method(cls): pass class Foo(object): __metaclass__ = MetaFoo #client.py from foo import Foo file_path = Foo.file_path I like this approach better than the first pattern for a few reasons: First, instantiating Foo would be meaningless as it has no attributes or methods, which insures this class acts like a true single interface utility, unlike the first pattern which relies on the underscore convention to dissuade client code from creating more instances of the internal class. Second, sub-classing MetaFoo in a different module wouldn't be as awkward because I wouldn't be importing a class with an underscore which is inherently going against its private naming convention. Third, this seems to be the closest approximation to a static class that exists in python, as all the meta code applies only to the class and not to its instances. This is shown by the common convention of using cls instead of self in the class methods. As well, the base class inherits from type instead of object which would prevent users from trying to use it as a base for other non-static classes. It's implementation as a static class is also apparent when using it by the naming convention Foo, as opposed to foo, which denotes a static class method is being used. As much as I think this is a good fit, I feel that others might feel its not pythonic because its not a sanctioned use for metaclasses which should be avoided 99% of the time. I also find most python devs tend to shy away from metaclasses which might affect code reuse/maintainability. Is this code considered code smell in the python community? I ask because I'm creating a pypi package, and would like to do everything I can to increase adoption.

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  • Examples of bad variable names and reasons [on hold]

    - by user470184
    I'll start with a class in the jdk package : public final class Sdp { should be : public final class SocketsDirectProtocol { Sdp is class name, this is ambigious, should be : Class<?> cl = Class.forName("java.net.SdpSocketImpl", true, null); should be : Class<?> clazz = Class.forName("java.net.SdpSocketImpl", true, null); cl is ambiguous private static void setAccessible(final AccessibleObject o) { should be : private static void setAccessible(final AccessibleObject accessibleObject) { There are various other examples in this class, do you have similar and/or differing examples of variables that were named badly ? package com.oracle.net; public final class Sdp { private Sdp() { } /** * The package-privage ServerSocket(SocketImpl) constructor */ private static final Constructor<ServerSocket> serverSocketCtor; static { try { serverSocketCtor = (Constructor<ServerSocket>) ServerSocket.class.getDeclaredConstructor(SocketImpl.class); setAccessible(serverSocketCtor); } catch (NoSuchMethodException e) { throw new AssertionError(e); } } /** * The package-private SdpSocketImpl() constructor */ private static final Constructor<SocketImpl> socketImplCtor; static { try { Class<?> cl = Class.forName("java.net.SdpSocketImpl", true, null); socketImplCtor = (Constructor<SocketImpl>)cl.getDeclaredConstructor(); setAccessible(socketImplCtor); } catch (ClassNotFoundException e) { throw new AssertionError(e); } catch (NoSuchMethodException e) { throw new AssertionError(e); } } private static void setAccessible(final AccessibleObject o) { AccessController.doPrivileged(new PrivilegedAction<Void>() { public Void run() { o.setAccessible(true); return null; } }); } /** * SDP enabled Socket. */ private static class SdpSocket extends Socket { SdpSocket(SocketImpl impl) throws SocketException { super(impl); } } /** * Creates a SDP enabled SocketImpl */ private static SocketImpl createSocketImpl() { try { return socketImplCtor.newInstance(); } catch (InstantiationException x) { throw new AssertionError(x); } catch (IllegalAccessException x) { throw new AssertionError(x); } catch (InvocationTargetException x) { throw new AssertionError(x); } } /** * Creates an unconnected and unbound SDP socket. The {@code Socket} is * associated with a {@link java.net.SocketImpl} of the system-default type. * * @return a new Socket * * @throws UnsupportedOperationException * If SDP is not supported * @throws IOException * If an I/O error occurs */ public static Socket openSocket() throws IOException { SocketImpl impl = createSocketImpl(); return new SdpSocket(impl); } /** * Creates an unbound SDP server socket. The {@code ServerSocket} is * associated with a {@link java.net.SocketImpl} of the system-default type. * * @return a new ServerSocket * * @throws UnsupportedOperationException * If SDP is not supported * @throws IOException * If an I/O error occurs */ public static ServerSocket openServerSocket() throws IOException { // create ServerSocket via package-private constructor SocketImpl impl = createSocketImpl(); try { return serverSocketCtor.newInstance(impl); } catch (IllegalAccessException x) { throw new AssertionError(x); } catch (InstantiationException x) { throw new AssertionError(x); } catch (InvocationTargetException x) { Throwable cause = x.getCause(); if (cause instanceof IOException) throw (IOException)cause; if (cause instanceof RuntimeException) throw (RuntimeException)cause; throw new RuntimeException(x); } } /** * Opens a socket channel to a SDP socket. * * <p> The channel will be associated with the system-wide default * {@link java.nio.channels.spi.SelectorProvider SelectorProvider}. * * @return a new SocketChannel * * @throws UnsupportedOperationException * If SDP is not supported or not supported by the default selector * provider * @throws IOException * If an I/O error occurs. */ public static SocketChannel openSocketChannel() throws IOException { FileDescriptor fd = SdpSupport.createSocket(); return sun.nio.ch.Secrets.newSocketChannel(fd); } /** * Opens a socket channel to a SDP socket. * * <p> The channel will be associated with the system-wide default * {@link java.nio.channels.spi.SelectorProvider SelectorProvider}. * * @return a new ServerSocketChannel * * @throws UnsupportedOperationException * If SDP is not supported or not supported by the default selector * provider * @throws IOException * If an I/O error occurs */ public static ServerSocketChannel openServerSocketChannel() throws IOException { FileDescriptor fd = SdpSupport.createSocket(); return sun.nio.ch.Secrets.newServerSocketChannel(fd); } }

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  • Cisco ASA 5510 ASDM: Setting up multiple public static ip addresses on a single interface and route

    - by ssjaken
    HI, i have a cisco ASA 5510 using ASDM version 6.3 We have a webserver that is been written very specifically and i was given super direct "DO NOT DEVIATE" directions. This server has to get traffic from 3 different PUBLIC ip's that we own. (our isp gave use a block of 12 static addresses) on 4 different ports. there are the directions i was given externalIP1:22 - 172.17.5.50:22 - SSH externalIP1:443 - 172.17.5.50:23040 - SIT externalIP2:443 - 172.17.5.50:33040 - STAGE externalIP3:443 - 172.17.5.50:43040 - PROD My first question is, using ASDM (my contract employer demands i use ASDM over CLI) how do i get three public addresses to work on one interface. We are authenticating on PPPoE. I know create a virtual interface with the static address but when i do i cannot ping the address from another offsite machine. secondly, where would i put the traffic redirect in. would i go ahead and create ACL's or just make NAT routes. Thanks.

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  • How do I configure an interface to have *both* a DHCP address and a static address in Ubuntu?

    - by Paul Hoffman
    In a lab setup, I want eth0 on a Ubuntu server box to get a DHCP address for talking to the outside world, and I also want to assign it a static 10.x.y.z address for talking to other boxes on the local network that have 10.x.y.z addresses. I want to do this by editing /etc/network/interfaces. The man page for /etc/network/interfaces is modeled after "here's a bunch of examples, I hope you can figure out the actual rules on your own". I don't see a way to give one interface two addresses using two different methods (static and dhcp), and initial fumbling didn't produce useful results.

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  • Does the OS X DHCP client support classless static routes (RFC3442)?

    - by cense
    Simply put: does Mac OS X support RFC3442? RFC3442 implements DHCP codes (121 and 249) to provide classless static routes to DHCP clients. I can only seem to find rather old information circa 2005-2008 which implies that OS X does not support RFC3442. Any chance this has changed recently and I'm just doing something wrong while setting it up? My anecdotal testing seems to confirm that OS X does not support RFC3442 but I'm looking for confirmation. If OS X still doesn't support RFC3442, what is an alternative method of pushing static routes to OS X clients?

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  • What happens to a PDF file when you save it as a static PDF file?

    - by JimDel
    Does anyone know what happens to a PDF file when you save it as a static PDF file? I have a 17K PDF file that doesn’t work will with my software. But when I save it as a Static PDF using Adobe Live Cycle, the file works just fine. But it’s significantly larger (327K). Because these file will be download over the web, I really want to keep the size down. I have hundreds of files like this. If I knew what happens to the file when it’s converted I might be in better shape. Thanks

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  • How to discharge static electricity before opening a computer?

    - by Pekka
    Before opening a computer, I often hear advice to touch something that is "grounded" - a computer case for example, or a heating element - to avoid damaging the sensitive electronic equipment through static discharge. What exactly is true here, and what are the do's and don'ts. Touching what objects will actually work, and what won't? If I touch a computer case, does it matter what it stands on, and whether it is connected to an outlet? What other ways are there to protect the equipment from a static discharge than touching something grounded? Are there common pieces of clothing that I shouldn't be wearing when working inside a computer, for example a woollen pullover? There is a lot on Google, but there seem to be many contradictions and misconceptions out there, so I think this is a question worth having here.

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  • How do I access an Ubuntu VirtualBox guest at a static IP from an OS X host?

    - by David Siegel
    How does one configure an Ubuntu guest to use a static IP that's visible to an OS X host, and ensure that the static IP is independent of the host's network configuration? I previously used bridged networking for my guest, but I'm constantly moving my host between networks so the guest IP is always different. First, I tried setting the guest network configuration to NAT and forwarding host port 1022 to guest port 22, so I could at least ssh to a fixed address (localhost:1022): $ VBoxManage setextradata "Ubuntu Server" "VBoxInternal/Devices/e1000/0/LUN#0/Config/SSH/Protocol" "TCP" $ VBoxManage setextradata "Ubuntu Server" "VBoxInternal/Devices/e1000/0/LUN#0/Config/SSH/GuestPort" 22 $ VBoxManage setextradata "Ubuntu Server" "VBoxInternal/Devices/e1000/0/LUN#0/Config/SSH/HostPort" 1022 Then, $ ssh localhost -p 1022 ssh: connect to host localhost port 1022: Connection refused But this didn't work (guest has no network access with NAT and OS X refused the connection, as you can see). I'd love a general solution that would let me communicate with my guest at a fixed IP.

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  • How do I access an Ubuntu VirtualBox guest at a static IP from an OS X host?

    - by David Siegel
    How does one configure an Ubuntu guest to use a static IP that's visible to an OS X host, and ensure that the static IP is independent of the host's network configuration? I previously used bridged networking for my guest, but I'm constantly moving my host between networks so the guest IP is always different. First, I tried setting the guest network configuration to NAT and forwarding host port 1022 to guest port 22, so I could at least ssh to a fixed address (localhost:1022): $ VBoxManage setextradata "Ubuntu Server" "VBoxInternal/Devices/e1000/0/LUN#0/Config/SSH/Protocol" "TCP" $ VBoxManage setextradata "Ubuntu Server" "VBoxInternal/Devices/e1000/0/LUN#0/Config/SSH/GuestPort" 22 $ VBoxManage setextradata "Ubuntu Server" "VBoxInternal/Devices/e1000/0/LUN#0/Config/SSH/HostPort" 1022 Then, $ ssh localhost -p 1022 ssh: connect to host localhost port 1022: Connection refused But this didn't work (guest has no network access with NAT and OS X refused the connection, as you can see). I'd love a general solution that would let me communicate with my guest at a fixed IP.

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