Asked  6 Months ago    Answers:  5   Viewed   27 times

What's difference between shadowing and overriding a method in C#?

 Answers

35

Well inheritance...

suppose you have this classes:

class A {
   public int Foo(){ return 5;}
   public virtual int Bar(){return 5;}
}
class B : A{
   public new int Foo() { return 1;}     //shadow
   public override int Bar() {return 1;} //override
}

then when you call this:

A clA = new A();
B clB = new B();

Console.WriteLine(clA.Foo()); // output 5
Console.WriteLine(clA.Bar()); // output 5
Console.WriteLine(clB.Foo()); // output 1
Console.WriteLine(clB.Bar()); // output 1

//now let's cast B to an A class
Console.WriteLine(((A)clB).Foo()); // output 5 <<<-- shadow
Console.WriteLine(((A)clB).Bar()); // output 1

Suppose you have a base class and you use the base class in all your code instead of the inherited classes, and you use shadow, it will return the values the base class returns instead of following the inheritance tree of the real type of the object.

Run code here

Hope I'm making sense :)

Tuesday, June 1, 2021
 
Isky
answered 6 Months ago
14

Encapsulation.

In the second instance you've just defined a variable, in the first, there is a getter / setter around the variable. So if you decide you want to validate the variable at a later date - it will be a lot easier.

Plus they show up differently in Intellisense :)

Edit: Update for OPs updated question - if you want to ignore the other suggestions here, the other reason is that it's simply not good OO design. And if you don't have a very good reason for doing it, always choose a property over a public variable / field.

Tuesday, June 1, 2021
 
employeegts
answered 6 Months ago
11

Magic Enum header-only library provides static reflection for enums (to string, from string, iteration) for C++17.

#include <magic_enum.hpp>

enum Color { RED = 2, BLUE = 4, GREEN = 8 };

Color color = Color::RED;
auto color_name = magic_enum::enum_name(color);
// color_name -> "RED"

std::string color_name{"GREEN"};
auto color = magic_enum::enum_cast<Color>(color_name)
if (color.has_value()) {
  // color.value() -> Color::GREEN
};

For more examples check home repository https://github.com/Neargye/magic_enum.

Where is the drawback?

This library uses a compiler-specific hack (based on __PRETTY_FUNCTION__ / __FUNCSIG__), which works on Clang >= 5, MSVC >= 15.3 and GCC >= 9.

Enum value must be in range [MAGIC_ENUM_RANGE_MIN, MAGIC_ENUM_RANGE_MAX].

  • By default MAGIC_ENUM_RANGE_MIN = -128, MAGIC_ENUM_RANGE_MAX = 128.

  • If need another range for all enum types by default, redefine the macro MAGIC_ENUM_RANGE_MIN and MAGIC_ENUM_RANGE_MAX.

  • MAGIC_ENUM_RANGE_MIN must be less or equals than 0 and must be greater than INT16_MIN.

  • MAGIC_ENUM_RANGE_MAX must be greater than 0 and must be less than INT16_MAX.

  • If need another range for specific enum type, add specialization enum_range for necessary enum type.

    #include <magic_enum.hpp>
    
    enum number { one = 100, two = 200, three = 300 };
    
    namespace magic_enum {
    template <>
      struct enum_range<number> {
        static constexpr int min = 100;
        static constexpr int max = 300;
    };
    }
    
Tuesday, June 1, 2021
 
Sidarta
answered 6 Months ago
31

I found something that at least begins to answer my own question. The following two links have wmv files from Microsoft that demonstrate using a C# class in unmanaged C++.

This first one uses a COM object and regasm: http://msdn.microsoft.com/en-us/vstudio/bb892741.

This second one uses the features of C++/CLI to wrap the C# class: http://msdn.microsoft.com/en-us/vstudio/bb892742. I have been able to instantiate a c# class from managed code and retrieve a string as in the video. It has been very helpful but it only answers 2/3rds of my question as I want to instantiate a class with a string perimeter into a c# class. As a proof of concept I altered the code presented in the example for the following method, and achieved this goal. Of course I also added a altered the {public string PickDate(string Name)} method to do something with the name string to prove to myself that it worked.

wchar_t * DatePickerClient::pick(std::wstring nme)
{
    IntPtr temp(ref);// system int pointer from a native int
    String ^date;// tracking handle to a string (managed)
    String ^name;// tracking handle to a string (managed)
    name = gcnew String(nme.c_str());
    wchar_t *ret;// pointer to a c++ string
    GCHandle gch;// garbage collector handle
    DatePicker::DatePicker ^obj;// reference the c# object with tracking handle(^)
    gch = static_cast<GCHandle>(temp);// converted from the int pointer 
    obj = static_cast<DatePicker::DatePicker ^>(gch.Target);
    date = obj->PickDate(name);
    ret = new wchar_t[date->Length +1];
    interior_ptr<const wchar_t> p1 = PtrToStringChars(date);// clr pointer that acts like pointer
    pin_ptr<const wchar_t> p2 = p1;// pin the pointer to a location as clr pointers move around in memory but c++ does not know about that.
    wcscpy_s(ret, date->Length +1, p2);
    return ret;
}

Part of my question was: What is better? From what I have read in many many efforts to research the answer is that COM objects are considered easier to use, and using a wrapper instead allows for greater control. In some cases using a wrapper can (but not always) reduce the size of the thunk, as COM objects automatically have a standard size footprint and wrappers are only as big as they need to be.

The thunk (as I have used above) refers to the space time and resources used in between C# and C++ in the case of the COM object, and in between C++/CLI and native C++ in the case of coding-using a C++/CLI Wrapper. So another part of my answer should include a warning that crossing the thunk boundary more than absolutely necessary is bad practice, accessing the thunk boundary inside a loop is not recommended, and that it is possible to set up a wrapper incorrectly so that it double thunks (crosses the boundary twice where only one thunk is called for) without the code seeming to be incorrect to a novice like me.

Two notes about the wmv's. First: some footage is reused in both, don't be fooled. At first they seem the same but they do cover different topics. Second, there are some bonus features such as marshalling that are now a part of the CLI that are not covered in the wmv's.

Edit:

Note there is a consequence for your installs, your c++ wrapper will not be found by the CLR. You will have to either confirm that the c++ application installs in any/every directory that uses it, or add the library (which will then need to be strongly named) to the GAC at install time. This also means that with either case in development environments you will likely have to copy the library to each directory where applications call it.

Wednesday, June 2, 2021
 
DiglettPotato
answered 6 Months ago
94

_Pragma operator introduced in C99. _Pragma(arg) is an operator, much like sizeof or defined, and can be embedded in a macro.

According to cpp.gnu.org reference:

Its syntax is _Pragma (string-literal), where string-literal can be either a normal or wide-character string literal. It is destringized, by replacing all \ with a single and all " with a ". The result is then processed as if it had appeared as the right hand side of a #pragma directive. For example,

 _Pragma ("GCC dependency "parse.y"")

has the same effect as #pragma GCC dependency "parse.y". The same effect could be achieved using macros, for example

 #define DO_PRAGMA(x) _Pragma (#x)
 DO_PRAGMA (GCC dependency "parse.y")

According to IBM tutorial:

The _Pragma operator is an alternative method of specifying #pragma directives. For example, the following two statements are equivalent:

#pragma comment(copyright, "IBM 2010")
_Pragma("comment(copyright, "IBM 2010")")

The string IBM 2010 is inserted into the C++ object file when the following code is compiled:

_Pragma("comment(copyright, "IBM 2010")")
int main() 
{
   return 0;
}

For more information about _pragma with example.

Tuesday, August 3, 2021
 
Oshrib
answered 4 Months ago
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