I have a code (in C++, but for other languages solution of problem is probably similar):
namespace details {
struct C {
/// Documentation for common method.
void c();
};
};
/// Documentation for class A
struct A: public details:C {
/// Documentation for method a
void a();
};
/// Documentation for class B
struct B: public details:C {
/// Documentation for method b
void b();
};
And I want to hide class C (and whole details namespace) in documentation (it exists only to make A and B implementation shorter). But I need to have A and B in documentation, with c member (and all other members inherited from C) documented, like for source:
/// Documentation for class A
struct A {
/// Documentation for method a
void a();
/// Documentation for common method.
void c();
};
/// Documentation for class B
struct B {
/// Documentation for method b
void b();
/// Documentation for common method.
void c();
};
How to do this properly?
Related
Why I cannot do that? I get compilation error.
public interface A {
void update(Object a);
}
public class B implements A{
void update(Long a) {
}
}
That is Java 8
I do not see here violating any OO principle.
That's really make my time difficult to implement a generic API...
(I try to get Generics out of the play because the generic API gets counter-intuitive)
You get a compilation error because void update(Long a) does not implement void update(Object a).
You can implement it as follows:
public class B implements A {
void update(Object o) {
if (!(o instanceof Long)) {
// possibly throw an exception
}
Long a = (Long) o;
...
}
}
A class that implements an interface must implement all the methods declared in the interface. The methods must have the exact same signature (name + parameters) as declared in the interface. The class does not need to implement (declare) the variables of an interface. Only the methods.
Source:
http://tutorials.jenkov.com/java/interfaces.html#:~:text=A%20class%20that%20implements%20an,Only%20the%20methods.
C++/CLI :
public interface class ITest{
public:
virtual void doSomething (){
}
}
public ref Base {
...........
...........
}
generic <typename T> where T : ITest
public ref Derived : Base{
public:
virtual void doNothing (){
}
}
public ref AnotherClass {
public:
generic<class T> where T : Base
static int justDoThis(){
//Problem!!
}
}
C# :
In C# there are two classes A and B. A inherits from the ITest and B inherits from Derived where A is used as the typename. Also, B has a private variable of type A. So, from main function AnotherClass.justDoThis<B>() is called where B is passed as the generic type.
"//Problem!!" Part :
Now I have to create a new instance of B in this section and also access the A which is private variable in B.
So if I take your paragraph of description of the C# code:
class A : ITest {}
class B : Derived<A>
{
private A someVariableOfTypeA;
}
class Program
{
void Main(string[] args)
{
AnotherClass.justDoThis<B>();
}
}
And the problem is that you want to do this:
public ref AnotherClass {
public:
generic<class T> where T : Base
static int justDoThis()
{
// Problem!!
Something^ actuallyB = gcnew Something();
A^ a = actuallyB->someVariableOfTypeA;
}
}
Issue #1: You can allow creation of new objects of the generic type by specifying gcnew as another generic constraint. (In C#, this would be new.) This will require that the generic type have a default (i.e., parameterless) constructor, which you can access with the normal gcnew.
generic<class T> where T : Base, gcnew
static int justDoThis()
{
T^ t = gcnew T();
}
Issue #2: You cannot access private variables within an object. That's what private means. If you want to give justDoThis access to the A object, then add an appropriate public method or property to Base. The method or property would return type ITest. You could also put that method/property on a new interface (perhaps named IHaveAnITestAccessorMethod), and add that as another generic constraint, and B satisfies all the constraints.
Note that it won't do any good to make the variable public on type B: justDoThis doesn't know about B, it only knows about T, which is a Base with a no parameter constructor.
Disclaimers:
I didn't check my syntax with a compiler.
Yes, you can do anything with reflection, but that's a bad design. Don't do that, fix your code the right way.
As far as I know you need to annotate a function this way:
#objc MyProtocol{
optional func yourOptionalMethod()
}
But why is it needed the #objc annotation?
From Apple Documentation:
NOTE
Optional protocol requirements can only be specified if your protocol
is marked with the #objc attribute.
This attribute indicates that the protocol should be exposed to
Objective-C code and is described in Using Swift with Cocoa and
Objective-C. Even if you are not interoperating with Objective-C, you
need to mark your protocols with the #objc attribute if you want to
specify optional requirements.
Note also that #objc protocols can be adopted only by classes, and not
by structures or enumerations. If you mark your protocol as #objc in
order to specify optional requirements, you will only be able to apply
that protocol to class types.
Please check Apple Documentation:
Also,
Optional protocol requirements can only be specified if your protocol is >marked with the #objc attribute.
This attribute indicates that the protocol should be exposed to >Objective-C code and is described in Using Swift with Cocoa and >Objective-C. Even if you are not interoperating with Objective-C, you >need to mark your protocols with the #objc attribute if you want to >specify optional requirements.
Note also that #objc protocols can be adopted only by classes, and not >by structures or enumerations. If you mark your protocol as #objc in >order to specify optional requirements, you will only be able to apply >that protocol to class types.
Again, explained here in Swift Documentation:
/// The protocol to which all types implicitly conform
typealias Any = protocol
/// The protocol to which all class types implicitly conform.
///
/// When used as a concrete type, all known `#objc` `class` methods and
/// properties are available, as implicitly-unwrapped-optional methods
/// and properties respectively, on each instance of `AnyClass`. For
/// example:
///
/// .. parsed-literal:
///
/// class C {
/// #objc class var cValue: Int { return 42 }
/// }
///
/// // If x has an #objc cValue: Int, return its value.
/// // Otherwise, return nil.
/// func getCValue(x: AnyClass) -> Int? {
/// return **x.cValue**
/// }
///
/// See also: `AnyObject`
typealias AnyClass = AnyObject.Type
/// The protocol to which all classes implicitly conform.
///
/// When used as a concrete type, all known `#objc` methods and
/// properties are available, as implicitly-unwrapped-optional methods
/// and properties respectively, on each instance of `AnyObject`. For
/// example:
///
/// .. parsed-literal:
///
/// class C {
/// #objc func getCValue() -> Int { return 42 }
/// }
///
/// // If x has a method #objc getValue()->Int, call it and
/// // return the result. Otherwise, return nil.
/// func getCValue1(x: AnyObject) -> Int? {
/// if let f: ()->Int = **x.getCValue** {
/// return f()
/// }
/// return nil
/// }
///
/// // A more idiomatic implementation using "optional chaining"
/// func getCValue2(x: AnyObject) -> Int? {
/// return **x.getCValue?()**
/// }
///
/// // An implementation that assumes the required method is present
/// func getCValue3(x: AnyObject) -> **Int** {
/// return **x.getCValue()** // x.getCValue is implicitly unwrapped.
/// }
///
/// See also: `AnyClass`
#objc protocol AnyObject {
}
I'm studying Visitor Pattern advantages, and quoting Design Patterns:
But an iteratorcan't work across object structures with different
types of elements. Forexample, the Iterator interface defined on page
295 can access only objects of type Item:
template <class Item>
clas Iterator { // ... Item CurrentItem() const; };
This implies that all elements the iterator can visit have a common parentclass Item.
Visitor does not have this restriction...
class Visitor {
public:
// ...
void VisitMyType(MyType*);
void VisitYourType(YourType*);
};
MyType and YourType do not have to be related throughinheritance at
all.
I agree about this quote, but I can't figure out an example where the Visitor Pattern could explore a structure (like a List) where objects collected in it are not related by a super class.
In other words, can you show me an example where the features above is true please?
First, you should know what these patterns are for.
The Iterator Pattern is used to access an aggregate sequentially without exposing its underlying representation. So you could Hide a List or array or similar aggregates behind an Iterator.
Visitor Pattern is used to perform an action on a structure of elements without changing the implementation of the elements themselves.
So you use the patterns in two different situations and not as alternatives to each other.
In the Visitor Pattern you implement an Interface IAcceptor in each element you want to visit. So the Visitor Pattern doesn't rely on a superclass but on Interfaces
public interface IAcceptor
{
public void Accept(IVisitor visitor);
}
So if you have a List of objects you can iterate over it and visit the objects implementing IAcceptor
public VisitorExample()
{
MyVisitorImplementation visitor = new MyVisitorImplementation();
List<object> objects = GetList();
foreach(IAcceptor item in objects)
item.Accept(visitor);
}
public interface IVisitor
{
public void Visit(MyAcceptorImplementation item);
public void Visit(AnotherAcceptorImplementation item);
}
public class MyAcceptorImplementation : IAcceptor
{
//Some Code ...
public void Accept(IVisitor visitor)
{
visitor.Visit(this);
}
}
To complete the code here is Visitor to write to Console if it visits my or another implementation of an acceptor.
public class MyVisitorImplementation : IVisitor
{
public void Visit(MyAcceptorImplementation item)
{
Console.WriteLine("Mine");
}
public void Visit(AnotherAcceptorImplementation item)
{
Console.WriteLine("Another");
}
}
For more useful examples and better explanation have a look at Visitor Pattern and Iterator Pattern
EDIT: Here an example using both, the visitor and Iterator. The iterator is just the logic how to move through your aggregate. It would make more sense with a hierarchical structure.
public VisitorExample2()
{
MyVisitorImplementation visitor = new MyVisitorImplementation();
List<object> myListToHide = GetList();
//Here you hide that the aggregate is a List<object>
ConcreteIterator i = new ConcreteIterator(myListToHide);
IAcceptor item = i.First();
while(item != null)
{
item.Accept(visitor);
item = i.Next();
}
//... do something with the result
}
There are two good examples I know of where visitor is clearly preferable to iterator.
The first is interacting with some unknown set of class members, in particular in C++. For example, here's a visitor that prints out all the members of other classes. Imagine you're the author of Printer and someone you're unacquainted with is the author of Heterogeneous3Tuple.
#include <iostream>
template<class ElemType1, class ElemType2, class ElemType3>
class Heterogeneous3Tuple
{
public:
Heterogeneous3Tuple(ElemType1 elem1, ElemType2 elem2, ElemType3 elem3)
: elem1_(std::move(elem1)), elem2_(std::move(elem2)), elem3_(std::move(elem3))
{}
template<class Visitor>
void accept(const Visitor& visitor)
{
visitor(elem1_);
visitor(elem2_);
visitor(elem3_);
}
private:
ElemType1 elem1_;
ElemType2 elem2_;
ElemType3 elem3_;
};
class Printer
{
public:
template<class VisitedElemType>
void operator()(const VisitedElemType& visitee) const
{
std::cout << visitee << std::endl;
}
private:
};
int main() {
Heterogeneous3Tuple<char, int, double> h3t('a', 0, 3.14);
Printer p;
h3t.accept(p);
}
a
0
3.14
coliru
There's no sensible way to get an iterator to work here. Without even knowing what types our Printer class might interact with this works so long as the visitor is accept()ed and the elements all interact in a similar way with operator << and a stream.
The other good example I know of shows up in abstract syntax tree manipulations. CPython and LLVM both use visitors. Using a visitor here prevents code that manipulates certain AST nodes from needing to know how to iterate over all the various AST nodes that might branch in complicated ways. The LLVM source code goes into more detail. Here's the highlight:
/// Instruction visitors are used when you want to perform different actions
/// for different kinds of instructions without having to use lots of casts
/// and a big switch statement (in your code, that is).
///
/// To define your own visitor, inherit from this class, specifying your
/// new type for the 'SubClass' template parameter, and "override" visitXXX
/// functions in your class. I say "override" because this class is defined
/// in terms of statically resolved overloading, not virtual functions.
///
/// For example, here is a visitor that counts the number of malloc
/// instructions processed:
///
/// /// Declare the class. Note that we derive from InstVisitor instantiated
/// /// with _our new subclasses_ type.
/// ///
/// struct CountAllocaVisitor : public InstVisitor<CountAllocaVisitor> {
/// unsigned Count;
/// CountAllocaVisitor() : Count(0) {}
///
/// void visitAllocaInst(AllocaInst &AI) { ++Count; }
/// };
///
/// And this class would be used like this:
/// CountAllocaVisitor CAV;
/// CAV.visit(function);
/// NumAllocas = CAV.Count;
I have begun to test Fluent NHibernate in C#
I have a well normalized object structure with 20 related classes.
I currently use Fluent 1.3 with NHibernate 3.2.
So far I have managed to use the AutoMap feature which suits me fine,
Very convenient!
BUT ...
3 of the tables are "enum tables" that need to have their records set with specific Id value.
I tried to make manual mappings of these tables and let the rest be automapped.
But when the manual table is created it fails because it references a table that is automapped (and not available for manual mapper?)
Is it possible to use AutoMapping but for some very few classes override identity creation on primary key?
I tried to make a custom convention but without success.
public class OverrideIdentityGeneration : Attribute
{
}
public class ConventionIdentity : AttributePropertyConvention<OverrideIdentityGeneration>
{
protected override void Apply(OverrideIdentityGeneration attribute, IPropertyInstance instance)
{
instance.Generated.Never();
}
}
Is there some other way?
It would be sad to be forced back to use manual mapping for all classes ....
class MyIdConvention : IIdConvention
{
public void Apply(IIdentityInstance instance)
{
if (instance.EntityType == ...)
{
instance.GeneratedBy.Assigned();
}
}
}
Update:
for enum-like classes it's often easier to define an enum as id
class ConfigValue
{
public virtual Config Id { get; set; }
}
// the convention is easy
if (instance.EntityType.IsEnum)
{
instance.GeneratedBy.Assigned();
// to save as int and not string
instance.CustomType(typeof(Config));
}
// querying without magic int values
var configValue = Session.Get<ConfigValue>(Config.UIColor);
I used the idea given by Fifo and extended it to use a custom attribute instead.
To make code readable and avoid redundance when using similar idea in other conventions I added an extension method to check for custom attribute.
This is the code I ended up with:
/// <summary>
/// Convention to instruct FluentNHIbernate to NOT generate identity columns
/// when custom attribute is set.
/// </summary>
public class ConventionIdentity : IIdConvention
{
public void Apply(IIdentityInstance instance)
{
if(instance.CustomAttributeIsSet<NoIdentity>())
instance.GeneratedBy.Assigned();
}
}
/// <summary>
/// Custom attribute definition.
/// </summary>
public class NoIdentity : Attribute
{
}
/// <summary>
/// Example on how to set attribute.
/// </summary>
public class Category
{
[NoIdentity]
public int Id { get; set; }
public string Name { get; set; }
}
public static class IInspectorExtender
{
/// <summary>
/// Extender to make convention usage easier.
/// </summary>
public static T GetCustomAttribute<T>(this IInspector instance)
{
var memberInfos = instance.EntityType.GetMember(instance.StringIdentifierForModel);
if(memberInfos.Length > 0)
{
var customAttributes = memberInfos[0].GetCustomAttributes(false);
return customAttributes.OfType<T>().FirstOrDefault();
}
return default(T);
}
}