Skip to main content

Cum putem sa verificam tipul unei variabile intr-un SWITCH

Sunt momente cand avem nevoie de a face anumite actiuni in functie de tipul variabilei. Din pacate SWITCH-ul nu ne permite acest lucru in mod direct si suntem nevoiți sa apelam la IF..ELSE.
if (item is int)
{...}
else if (item is string)
{...}
else if (item is DateTime)
{...}
else if (item is ...)
Codul pe care il obtinem nu este foarte lizibil. Daca totusi am vrea sa folosim SWITCH am fi nevoiti sa lucram cu string-uri obtinand ceva asemanator cu:
swtich( v.GetType().Name)
{
case typeof(int).Name:
...
break;
case typeof(DateTime).Name:
...
break;
...
}
Parca e mai bine decat codul precedent, dar ceea ce nu e tocmai bine este ca lucram cu string-uri. O solutie la aceasta problema este sa folosim TypeCode. Acest enum contine toate tipurile built-in din .NET.
switch( Type.GetTypeCode(v.GetType)))
{
case TypeCode.Int32:
...
break;
case TypeCode.DateTime:
...
break;
...
}
In cazul in care lucram doar cu tipurile built-in din .NET totul este perfect. Ceea ce imi place la TypeCode este ca are valori precum "Empty" sau "DBNull". Dar ce ne facem daca lucram cu vectori, cu liste generice sau cu entități proprii. In acest caz TypeCode nu mai poate fi folosit. Pentru acest caz eu am gasit doua rezolvari. O solutie este sa ne folosim de un dicționar de forma:
Dictionary<Type, int>
sau
Dictionary<Type, [CustomEnum]>
In cazul acesta am putea sa adaugam la initializarea dictionarului toate tipurile cu care lucram, iar apoi sa scriem un switch asemanator cu acesta:
swtich( types[v.GetType()])     // types - este o instanta a dictionarului in care avem toate tipurile cu care lucram.
{
case 0: //sau case CustomEnum.Int32
...
break;
case 1: //sau case CustomEnum.DateTime
...
break;
...
}
Urmatoarea solutie pe care o propun este sa ne definim o clasa CustomSwitch iar pentru fiecare case in parte sa ne definim actiunea dorita. Putem sa ne definim modelul si intr-un mod fluent, a.i. la final sa putem aveam ceva asemanator cu:
var customSwitch = new CustomSwitch(v)
.Case<int>( x => ...actiune... );
.Case<DateTime>( x => ...actiune... );
Mai jos puteti sa gasiti implemenentarea pentru CustomSwitch:
public class CustomSwitch
{
public CustomSwitch(Object obj)
{
Obj = obj;
}

public Object Obj { get; set; }
}
public static class CustomSwitchExtensions
{
public static CustomSwitch Case<T>( this CustomSwitch cs,Action<T> action)
where T : class
{
var obj = s.Obj as T;
if (obj != null)
{
action(obj);
return null;
}
}
}
La aceasta implementare s-ar mai putea adauga si un flag care sa permita un mecanism de fall through si prin celelalte case-uri. Din cele doua variante propuse as alege a doua varianta doar in cazul in care as avea nevoie si de un mecanism de fall through. De exemplu in cazul in care as avea nevoie sa execut doua case-uri pentru un obiect( ex. in cazul in care implementateaza interfata IA o actiune, si pentru interfata IB o alta actiune).

Comments

  1. :) Daca faci switch pe type ai o problema mult mai mare decat "cum sa faci". Think polymorphism :)

    ReplyDelete

Post a Comment

Popular posts from this blog

How to check in AngularJS if a service was register or not

There are cases when you need to check in a service or a controller was register in AngularJS.
For example a valid use case is when you have the same implementation running on multiple application. In this case, you may want to intercept the HTTP provider and add a custom step there. This step don’t needs to run on all the application, only in the one where the service exist and register.
A solution for this case would be to have a flag in the configuration that specify this. In the core you would have an IF that would check the value of this flag.
Another solution is to check if a specific service was register in AngularJS or not. If the service was register that you would execute your own logic.
To check if a service was register or not in AngularJS container you need to call the ‘has’ method of ‘inhector’. It will return TRUE if the service was register.
if ($injector.has('httpInterceptorService')) { $httpProvider.interceptors.push('httpInterceptorService&#…

ADO.NET provider with invariant name 'System.Data.SqlClient' could not be loaded

Today blog post will be started with the following error when running DB tests on the CI machine:
threw exception: System.InvalidOperationException: The Entity Framework provider type 'System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer' registered in the application config file for the ADO.NET provider with invariant name 'System.Data.SqlClient' could not be loaded. Make sure that the assembly-qualified name is used and that the assembly is available to the running application. See http://go.microsoft.com/fwlink/?LinkId=260882 for more information. at System.Data.Entity.Infrastructure.DependencyResolution.ProviderServicesFactory.GetInstance(String providerTypeName, String providerInvariantName) This error happened only on the Continuous Integration machine. On the devs machines, everything has fine. The classic problem – on my machine it’s working. The CI has the following configuration:

TeamCity.NET 4.51EF 6.0.2VS2013
It seems that there …

Fundamental Books of a Software Engineer (version 2018)

More then six years ago I wrote a blog post about fundamental books that any software engineer (developer) should read. Now it is an excellent time to update this list with new entries.

There are 5 different categories of books, that represent the recommended path. For example, you start with Coding books, after that, you read books about Programming, Design and so on.
There are some books about C++ that I recommend not because you shall know C++, only because the concepts that you can learn from it.

Coding

Writing solid codeCode completeProgramming Pearls, more programming pearls(recommended)[NEW] Introduction to Algorithms

Programming

Refactoring (M. Fowler)Pragmatic ProgrammerClean code[NEW] Software Engineering: A Practitioner's Approach[NEW] The Mythical Man-Month[NEW] The Art of Computer Programming

Design

Applying UML and Patterns (GRASP patterns)C++ coding standards (Sutter, Alexandrescu)The C++ programming language (Stroustrup, Part IV)Object-oriented programming (Peter Coad)P…