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Invoking methods with out and ref – Finale !!!

Alright, it is a long wait. And I am going to keep it short.

Recap of the problem: Why did the ref variable in SomeMethod not get the expected result (DayOfWeek.Friday) when called from a different thread?

Boxing. Yes, that is the culprit. Sometimes, it is subtle to note. DayOfWeek is an enum – a value type. When the method is called from a different thread, we put the argument (arg3) in an object array, and that’s where the value gets boxed. So we happen to assign the resultant value to the boxed value.

Invoking methods with Out and Ref (Part 2) !!!

Straight to code…..

int SomeMethod(string arg1,
    string arg2,
    ref DayOfWeek arg3)
{
    // Wildest implementation!
}

The above method had to be executed on its dispatcher thread. So let unravel a bit of the wildest implementation above.

int SomeMethod(string arg1,
    string arg2,
    ref DayOfWeek arg3)
{
    if (Disptacher.CheckAccess())
    {
        var funcDelegate = (Func<string, string, DayOfWeek, int>)SomeMthod;
    return Dispatcher.Invoke(funcDelegate,
        arg1,
        arg2,
        ref arg3);
}

// Wilder implementation!!

}

Before you say anything, yes, the compiler spat the following errors:-

Thinking Currying

Currying is a mathematical concept based on lambda calculus. It is a technique of operating on a function (taking multiple arguments) by splitting and capable of chaining into a series of single argument functions. It is very similar to what a human would attempt to do on paper. For example, if you have to add numbers 1 through 10, what would you do? Class II mathematics -0 in hand, 1 in the mind, add 0 and 1, so 1 in the mind, then 2 in the hand, … up to 10. So we compute the addition with one argument at a time. More ...

Quiz – (Journey through templates, SFINAE and specialization) !!!

template<typename A, typename B>
class TClass
{
public: TClass()
        {
        }

        // Overload #1
public: std::string SomeMethod(A a, B b)
        {
           std::ostringstream ostr;
           ostr << a << "-" << b;
           return ostr.str();
        }

        // Overload #2
public: std::string SomeMethod(B b, A a)
        {
           std::ostringstream ostr;
           ostr << b << "-" << a;
           return ostr.str();
        }
};

So that is a template class with SomeMethod overloads. Why would somebody write such a class? Imagine it is an adder class, and the method overloads could used to add with parameters specified in either order. Following is the way one could use the above (based on the adder example):-

Missing MI !!!

We all know C# does not offer multiple inheritance but offers arguments that programmers can live without it. It is true in almost all cases, especially all cat and animal or employee and manager projects. I have seen a few cases where if C# offered multiple inheritance, the solution would have been natural, elegant and succinct.

Imagine that I have a component (UI, non-UI, doesn’t matter). You can make calls into the component, which does some interesting work for you. Imagine that the component takes an interface IComponentCallback to notify its parent. So I would do is have my parent class derive from IComponentCallback interface and pass this to the component. The code would look something like this:-

sizeof vs Marshal.SizeOf !!!

There are two facilities in C# to determine the size of a type – sizeof operator andMarshal.SizeOf method. Let us discuss what they offer and how they differ.

Before we settle the difference between sizeof and Marshal.SizeOf, let us discuss why would we want to compute the size of a variable or type. Other than academic, one typical reason to know the size of a type (in a production code) would be allocate memory for an array of items; typically done while using malloc. Unlike in C++ (or unmanaged world), computing the size of a type definitely has no such use in C# (managed world). Within the managed application, size does not matter; since there are types provided by the CLR for creating \ managing fixed size and variable size (typed) arrays. And as per MSDN, the size cannot be computed accurately. Does that mean we don’t need to compute the size of a type at all when working in the CLR world? Obviously no, else I would not be writing this post.

Curious Case Of Anonymous Delegates !!!

Senthil has left us thrilled in his new post, and also inspired me to write about the topic. Although, anonymous delegates have become a mundane stuff amongst programmers, there is still these subtle stuff left unexplored. Alright, let us try to answer Senthil’s question before he unravels the mystery in his next post.

A delegate is identified by its target. The target is the method to be executed on a delegate invocation and its associated instance or type. If the target is an instance method, the delegate preserves the target method pointer and the object instance. If the target is a static method, the delegate preserves the target method pointer and the type to which it belongs. So when a code like the one below to register a method to an event (or multicast delegate) is executed, a delegate object (EventHandler here) with the target information embedded is created and added to the invocation list of the event (or multicast delegate, KeyPressed here).

finally and Return Values !!!

Let us read some code:-

int SomeMethod()
{
    int num = 1;

    try
    {
        num = 5;
        return num;
    }
    finally
    {
        num += 5;
    }
}

What is the return value of SomeMethod? Some anonymous guy asked that question in the code project forum, and it has been answered. I am writing about it here because it is interesting and subtle. One should not be surprised when people misinterpret finally. So let us take a guess, 10 (i = 5, then incremented by 5 in the finally block).It is not the right answer; rather SomeMethod returns 5. Agreed that finally is called in all cases of returning from SomeMethod but the return value is calculated when it is time to return from SomeMethod, normally or abnormally. The subtlety lies not in the way finally is executed but in the return value is calculated. So the return value (5) is decided when a return is encountered in the try block. The finally is just called for cleanup; and the num modified there is local to SomeMethod. So make the return value 10, it is no use being hasty making SomeMethod return from the finally block. Because returning from finally is not allowed. (We will talk about it later why returning from catch block is a bad practice and why can’t we return from finally block). Had such modifications been done on a reference type, they would have been visible outside of SomeMethod, although the return value may be different.

Type Safe Logger

Article co-authored with Sanjeev, and published on CodeProject

PROBLEM

Every application logs a whole bunch of diagnostic messages, primarily for (production) debugging, to the console or the standard error device or to files. There are so many other destinations where the logs can be written to. Irrespective of the destination that each application must be able to configure, the diagnostic log message and the way to generate the message is of our interest now. So we are in need of a logger class that can behave transparent to the logging destination. That should not be a problem, it would be fun to design that.

Simple Array Class For C++

This is a simple array like class for C++, which can be used as a safe wrapper for accessing a block of memory pointed by a bare pointer.