I have SomeBigFlow that calls multiple subflows inside it i.e ValidateFlowA, ValidateFlowB. Assuming it is mandatory for A and B to be initiating flows not functions.
How do I mock a return value for ValidateFlowA when I run the SomeBigFlow in Junit?
I've seen some references to using registerAnswer to mock flows' return value here. I am also curious why this function is only available for InternalMockNetwork.MockNode but not MockNetwork.StartedMockNode which is typically used during junit testing)
I thought I could replicate it by having node[1].registerAnswer(ValidateFlowA.class, 20). But when I ran node[1].startFlow(SomeBigFlow).resultFuture.getOrThrow(), the ValidateFlowA is still using its default call implementation instead of returning the mocked 20 integer value. Maybe I'm using it wrong.
Any pointers on how to make this work or is there a solution to achieve mocking inlined subflows returned values? The only other way I can think of is have a rule of thumb that whenever calling an inlined subflow, put them in an open fun that can be overridden during mocknetwork testing - this makes inlined subflow tedious, hoping for a neater way.
For now, you'd have to use a similar approach to the one outlined here: Corda with mockito_kotlin for unit test.
In summary:
Make the FlowLogic class you are testing open, and move the call to the subflow into an open method
For testing, create a subclass of the open FlowLogic class where you override the open method to return a dummy result
Use this subclass in testing
The answer
"Calling a non-virtual function will use the function from the same class as the pointer type, regardless of whether the object was actually created as some other derived type. Whereas calling a virtual function will use the function from the original allocated object type, regardless of what kind of pointer you're using."
was the best to me in the question link
What are the differences between overriding virtual functions and hiding non-virtual functions?
However, I still don't see the benefits of making a function virtual. Why not just make it concrete and override the function when necessary?
All the answers in your link are pretty complicated, since they actually answer more questions than actually asked :-)
I try to make it easier (lets hope for the best):
The concept of a virtual function allows you to guarantee that whatever pointer you use (see the example in the link Parent* p2 or Child* cp) on a class with some inheritance involved, it will always call the "youngest" child's implementation in the inheritance chain.
Example: If you have "child -> parent" and "grandchild -> child -> parent" with exact same function f2() definitions and all virtual, you can now assume that "grandchild::f2" is called in all circumstances. If you omitted the "virtual" keyword in your parent, you would have different functions being called, depending on which pointer you use to access the instance.
So. What is this useful for? Imagine you have a template based collection and want to put children inside the collection that is defined as parent-type collection list<Parent*>. If you now call a function on an element you fetch from the list, you can expect the child's function (definition) to be called! If you omit the "virtual" keyword in the f2() definition, the parents function is going to be called, which might be unexpected/undesired in most cases.
Any better? :-)
I'm a fairly new Ada programmer. I have read the book by Barnes (twice I might add) and even managed to write a fair terminal program in Ada. My main language is C++ though.
I am currently wondering if there is a way to "protect" subroutine calls in Ada, perhaps in Ada 2012 (of which I know basically nothing). Let me explain what I mean (although in C++ terms).
Suppose you have a class Secret like this:
class Secret
{
private:
int secret_int;
public:
Set_Secret_Value( int i );
}
Now this is the usual stuff, dont expose secret_int, manipulate it only through access functions. However, the problem is that anybody with access to an object of type Secret can manipulate the value, whether that particular code section is supposed to do it or not. So the danger of rogue altering of secret_int has been reduced to anybody altering secret_int through the permitted functions, even if it happens in a code section that's not supposed to manipulate it.
To remedy that I came up with the following construct
class Secret
{
friend class Secret_Interface;
private:
int secret_int;
Set_Secret_Value( int i );
Super_Secret_Function();
};
class Secret_Interface
{
friend class Client;
private:
static Set_Secret_Value( Secret &rc_secret_object, int i )
{
rc_secret_object.Set_Secret( i );
}
};
class Client
{
Some_Function()
{
...
Secret_Interface::Set_Secret_Value( c_object, some-value );
...
}
}
Now the class Secret_Interface can determine which other classes can use it's private functions and by doing so, indirectly, the functions of class Secret that are exposed to Secret_Interface. This way class Secret still has private functions that can not be called by anybody outside the class, for instance function Super_Secret_Function().
Well I was wondering if anything of this sort is possible in Ada. Basically my desire is to be able to say:
Code A may only be executed by code B but not by anybody else
Thanks for any help.
Edit:
I add a diagram here with a program structure like I have in mind that shows that what I mean here is a transport of a data structure across a wide area of the software, definition, creation and use of a record should happen in code sections that are otherwise unrleated
I think the key is to realize that, unlike C++ and other languages, Ada's primary top-level unit is the package, and visibility control (i.e. public vs. private) is on a per-package basis, not a per-type (or per-class) basis. I'm not sure I'm saying that correctly, but hopefully things will be explained below.
One of the main purposes of friend in C++ is so that you can write two (or more) closely related classes that both take part in implementing one concept. In that case, it makes sense that the code in one class would be able to have more direct access to the code in another class, since they're working together. I assume that in your C++ example, Secret and Client have that kind of close relationship. If I understand C++ correctly, they do all have to be defined in the same source file; if you say friend class Client, then the Client class has to be defined somewhere later in the same source file (and it can't be defined earlier, because at that point the methods in Secret or Secret_Interface haven't yet been declared).
In Ada, you can simply define the types in the same package.
package P is
type Secret is tagged private;
type Client is tagged private;
-- define public operations for both types
private
type Secret is tagged record ... end record;
type Client is tagged record ... end record;
-- define private operations for either or both types
end P;
Now, the body of P will contain the actual code for the public and private operations of both types. All code in the package body of P has access to those things defined in P's private part, regardless of which type they operate on. And, in fact, all code has access to the full definitions of both types. This means that a procedure that operates on a Client can call a private operation that operates on a Secret, and in fact it can read and write a Secret's record components directly. (And vice versa.) This may seem bizarre to programmers used to the class paradigm used by most other OOP languages, but it works fine in Ada. (In fact, if you don't need Secret to be accessible to anything else besides the implementation of Client, the type and its operations can be defined in the private part of P, or the package body.) This arrangement doesn't violate the principles behind OOP (encapsulation, information hiding), as long as the two types are truly two pieces of the implementation of one coherent concept.
If that isn't what you want, i.e. if Secret and Client aren't that closely related, then I would need to see a larger example to find out just what kind of use case you're trying to implement.
MORE THOUGHTS: After looking over your diagram, I think that the way you're trying to solve the problem is inferior design--an anti-pattern, if you will. When you write a "module" (whatever that means--a class or package, or in some cases two or more closely related classes or packages cooperating with each other), the module defines how other modules may use it--what public operations it provides on its objects, and what those operations do.
But the module (let's call it M1) should work the same way, according to its contract, regardless of what other module calls it, and how. M1 will get a sequence of "messages" instructing it to perform certain tasks or return certain information; M1 should not care where those messages are coming from. In particular, M1 should not be making decisions about the structure of the clients that use it. By having M1 decree that "procedure XYZ can only be called from package ABC", M1 is imposing structural requirements on the clients that use it. This, I believe, causes M1 to be too tightly coupled to the rest of the program. It is not good design.
However, it may make sense for the module that uses M1 to exercise some sort of control like that, internally. Suppose we have a "module" M2 that actually uses a number of packages as part of its implementation. The "main" package in M2 (the one that clients of M2 use to get M2 to perform its task) uses M1 to create a new object, and then passes that object to several other packages that do the work. It seems like a reasonable design goal to find a way that M2 could pass that object to some packages or subprograms without giving them the ability to, say, update the object, but pass it to other packages or subprograms that would have that ability.
There are some solutions that would protect against most accidents. For example:
package M1 is
type Secret is tagged private;
procedure Harmless_Operation (X : in out Secret);
type Secret_With_Updater is new Secret with null record;
procedure Dangerous_Operation (X : in out Secret_With_Updater);
end M1;
Now, the packages that could take a "Secret" object but should not have the ability to update it would have procedures defined with Secret'Class parameters. M2 would create a Secret_With_Updater object; since this object type is in Secret'Class, it could be passed as a parameter to procedures with Secret'Class parameters. However, those procedures would not be able to call Dangerous_Operation on their parameters; that would not compile.
A package with a Secret'Class parameter could still call the dangerous operation with a type conversion:
procedure P (X : in out Secret'Class) is
begin
-- ...
M1.Secret_With_Updater(X).Dangerous_Operation;
-- ...
end P;
The language can't prevent this, because it can't make Secret_With_Updater visible to some packages but not others (without using a child package hierarchy). But it would be harder to do this accidentally. If you really wish to go further and prevent even this (if you think there will be a programmer whose understanding of good design principles is so poor that they'd be willing to write code like this), then you could go a little further:
package M1 is
type Secret is tagged private;
procedure Harmless_Operation (X : in out Secret);
type Secret_Acc is access all Secret;
type Secret_With_Updater is tagged private;
function Get_Secret (X : Secret_With_Updater) return Secret_Acc;
-- this will be "return X.S"
procedure Dangerous_Operation (X : in out Secret_With_Updater);
private
-- ...
type Secret_With_Updater is tagged record
S : Secret_Acc;
end record;
-- ...
end M1;
Then, to create a Secret, M2 would call something that creates a Secret_With_Updater that returns a record with an access to a Secret. It would then pass X.Get_Secret to those procedures which would not be allowed to call Dangerous_Operation, but X itself to those that would be allowed. (You might also be able to declare S : aliased Secret, declare Get_Secret to return access Secret, and implement it with return X.S'access. This may avoid a potential memory leak, but it may also run into accessibility-check issues. I haven't tried this.)
Anyway, perhaps some of these ideas could help accomplish what you want to accomplish without introducing unnecessary coupling by forcing M1 to know about the structure of the application that uses it. It's hard to tell because your description of the problem, even with the diagram, is still at too abstract a level for me to see what you really want to do.
You could do this by using child packages:
package Hidden is
private
A : Integer;
B : Integer;
end Hidden;
and then
package Hidden.Client_A_View is
function Get_A return Integer;
procedure Set_A (To : Integer);
end Hidden.Client_A_View;
Then, Client_A can write
with Hidden.Client_A_View;
procedure Client_A is
Tmp : Integer;
begin
Tmp := Hidden.Client_A_View.Get_A;
Hidden.Client_A_View.Set_A (Tmp + 1);
end Client_A;
Your question is extremely unclear (and all the C++ code doesn't help explaining what you need), but if your point is that you want a type to have some publicly accessible operations, and some private operations, then it is easily done:
package Example is
type Instance is private;
procedure Public_Operation (Item : in out Instance);
private
procedure Private_Operation (Item : in out Instance);
type Instance is ... -- whatever you need it to be
end Example;
The procedure Example.Private_Operation is accessible to children of Example. If you want an operation to be purely internal, you declare it only in the package body:
package body Example is
procedure Internal_Operation (Item : in out Instance);
...
end Example;
Well I was wondering if anything of this sort is possible in Ada. Basically my desire is to be able to say:
Code A may only be executed by code B but not by anybody else
If limited to language features, no.
Programmatically, code execution can be protected if the provider must be provided an approved "key" to allow execution of its services, and only authorized clients are supplied with such keys.
Devising the nature, generation, and security of such keys is left as an exercise for the reader.
Similar questions have been raised multiple times, but I'm focussing on the namespace and pointer issues.
MyClass.h
namespace foo {
class MyClass {
MyClass();
};
QDataStream &operator<<(QDataStream &out, const MyClass & myObj);
QDataStream &operator>>(QDataStream &in, MyClass &myObj);
} // namespace foo
Q_DECLARE_METATYPE(foo::MyClass) // #1
Q_DECLARE_METATYPE(foo::MyClass*) // #2
fooMyClass.cpp (so many permutations):
MyClass::MyClass()
{
qRegisterMetaType<MyClass>("MyClass"); // #3
qRegisterMetaType<MyClass*>("MyClass*"); // #4
qRegisterMetaType<MyClass>("foo::MyClass"); // #5
qRegisterMetaType<MyClass*>("foo::MyClass*"); // #6
qRegisterMetaType<foo::MyClass>("foo::MyClass"); // #7
qRegisterMetaType<foo::MyClass*>("foo::MyClass*"); // #8
qRegisterMetaType<MyClass>(); // #9
qRegisterMetaType<MyClass*>(); // #10
qRegisterMetaType<foo::MyClass>(); // #11
qRegisterMetaType<foo::MyClass*>(); // #12
// same for qRegisterMetaTypeStreamOperators<T>();
}
So my question is, when and why is it required to provide the namespace and/or the pointer variant if I intend to use the custom objects for signals and slots (potentially as reference and pointer) inside as well as outside the namespace. Do I always have to fully qualify the namespace?
I'm referring to Qt5 in this answer. Qt4 doesn't go well with this use case.
Data stream operators
Data stream operators are not required for your type if you only intend to use it in signals and slots. They are required if you want to do some serialization.
Pointers, references and values
Qt considers MyClass and MyClass* two different unrelated types. You should declare, register and use them separately. Using const MyClass & argument type is compatible with MyClass in Qt meta-object system. Note that using MyClass and MyClass* meta types simultaneously in one program is unusual and can cause mistakes and confusion. You should choose one of the options and use it throughout the program. Also passing pointers to slots is not recommended because it causes unsolvable ownership problem. So I recommend to use passing by const reference (which sometimes will be converted to passing by value internally in Qt signal-slot system). If MyClass objects contain massive data, you should implement implicit data sharing using QSharedDataPointer.
Declaring a meta type
First of all, you always need to declare your meta type:
Q_DECLARE_METATYPE(foo::MyClass)
It works at compile time, so there are no limitations on how you refer to your class. The following code will work as well:
using namespace foo;
Q_DECLARE_METATYPE(MyClass)
Registering a meta type
Now you need to register your classes. Theoretically, you need to specify all strings that you want to use to refer to your type, i.e.:
qRegisterMetaType<foo::MyClass>("MyClass");
qRegisterMetaType<foo::MyClass>("foo::MyClass");
It doesn't matter how you refer to MyClass in the template argument. The following code will work similarly:
using namespace foo;
qRegisterMetaType<MyClass>("MyClass");
qRegisterMetaType<MyClass>("foo::MyClass");
For example, the "MyClass" and "foo::MyClass" strings are used to identify argument types when you refer to your signals and slots like SIGNAL(signal1(MyClass)).
New signal and slot syntax
If you using new signal slot syntax with pointers to member functions, you need to do only one registration with arbitrary string argument. It seems that it is intended to make it work even without any registrations. This part of the docs instructs to only add Q_DECLARE_METATYPE, in opposite to this that requires qRegisterMetaType(). Unfortunately, now in my Qt installation it works only with direct connections. Queued connections still require at least one registration call.
Implicit registration of class without namespace
I was experimenting with some variants of registration in Qt 5.1 and found out that Qt automatically registers aliases without namespace. So if you write
qRegisterMetaType<foo::MyClass>("foo::MyClass");
, Qt will additionally automatically register "MyClass" alias. So, after executing this statement you will be able to refer to your type as MyClass and foo::MyClass. There is no information in the documentation about how Qt handles namespaces. We could assume that this behavior is intended and will not be removed in next versions but I wouldn't rely on that. The following code makes implicit registration obvious:
qRegisterMetaType<foo::MyClass>("foo::MyClass");
qRegisterMetaType<bar::MyClass>("MyClass");
Qt 5.1 says:
QMetaType::registerTypedef: Binary compatibility break -- Type name 'MyClass' previously registered as typedef of 'MyClass' [1030], now registering as typedef of 'bar::MyClass' [1032].
Qt 4.8 works without error (it seems that this behavior is not yet introduced in this version).
I am trying to understand better reflection in Smalltalk. I am using the latest version of Squeak (v4.3). I want to intercept every message sent to instances of one of my classes. I assumed that I could override the method ProtoObject>>withArgs:executeMethod but Stéphane Ducasse explained me that for performance reason, this method is not used (this is my own summary of his answer). Which method should I override / how could intercept sent messages?
Here is the code of my attempt:
Object subclass: #C
instanceVariableNames: 'i'
classVariableNames: ''
poolDictionaries: ''
category: 'CSE3009'.
C class compile: 'newWithi: anInt
^(self new) i: anInt ; yourself.'.
C compile: 'withArgs: someArgs executeMethod: aMethod
Transcript show: ''Caught: ''.
^ super withArgs: someArgs executeMethod aMethod.'.
C compile: 'foo: aText
Transcript show: aText.
Transcript show: i.
Transcript cr.'.
C compile: 'i: anInt
i := anInt.'.
o := C newWithi: 42.
o foo: 'This is foo: '.
Executing this entire piece of code yields:
This is foo: 42
When I would like to have:
Caught: This is foo: 42
There's no build-in way to intercept messages to objects like that. There are two ways we commonly use to do this kind of trick.
First, you can create a wrapper object which responds to doesNotUnderstand:. This object usually has nil for the superclass so it doesn't inherit any instance methods from Object. The doesNotUnderstand: handler would delegate all its messages to the target object. It has the option of performing code before and after the call. All references to the original object would now point to the new "proxy" object. Messages to self wouldn't be intercepted and the proxy would need to test for objects that return self and change the returned object to be the proxy instead.
The second approach is to use a mechanism called Method Wrappers. Method Wrappers allows you to replace all of the methods in a set of classes with methods that do some other operations before and after calling the original method. This approach can provide fairly seemless results and intercepts all messages including those send to self.
MethodWrappers is available for VisualWorks and VASmalltalk. I believe it's also available for Squeak and Pharo but I'm not positive.
The three main techniques are:
Dynamic proxies
Method wrapper
Bytecode instrumentation
For a good comparision of all possible approaches, have a look at "Evaluating Message Passing Control Techniques in Smalltalk" by Stephane Ducasse (you already know him, apparently).
Of interest is also "Smalltalk: A Reflective Langauge" by F. Rivard, that shows how to implement pre- and post-conditions using bytecode rewriting. This is also a form of interception.