Skip to main content

Applications bugs that can be caused by 'ref' keyword

Zilele acestea ma uitam peste un cod si am intalnit urmatoarea linie de cod:
Foo foo1 = new Foo();
Foo foo2 = foo1;
DoSomeAction(ref foo1)
    foo1 = new Foo();
Pentru unele cazuri se ajungea ca in interiorul metodei DoSomeAction sa se creeze o noua instanta a obiectului Foo. Iar in unele cazuri aplicatia crapa intr-o alta locatie destul de urat. Nu o sa incep sa explic ce face keyword-ul ref si out.
Totusi am adaugat un citiat din MSDN ca sa pornim de la un punct comun.
The ref keyword causes an argument to be passed by reference, not by value. The effect of passing by reference is that any change to the parameter in the method is reflected in the underlying argument variable in the calling method. The value of a reference parameter is always the same as the value of the underlying argument variable. An argument that is passed to a ref parameter must be initialized before it is passed. This differs from out parameters, whose arguments do not have to be explicitly initialized before they are passed. For more information

Problema care apare in acest caz apare atat in cazul la ref cat si in out, dar in cazul la out. In momentul cand s-a facut atribuirea "foo2 = foo1", adresa de memorie spre care bate foo2 o sa fie aceiasi cu foo1. In interiorul metodei DoSomeAction ajungem sa cream un nou obiect de tip Foo, iar adresa de memorie spre care puncteaza foo1 se schimba cu o valoare noua. Dar foo2 o sa continue sa puncteze spre vechia adresa din memorie.
Din aceasta cauza foo2 ajunge sa puncteze spre vechia valoare, iar foo1 spre noua valoare.
Acest comportament este normal pentru ref si out, nu este nici o anomalie a limbajului. Intrebarea mea este urmatoare: Codul scris mai sus face ce ar trebui sa faca?
Raspunsul meu este ca NU. Daca vrem sa inlocuim un obiect cu alt obiect trebuie sa avem grija sa facem update la toate referintele acestuia sau poate nu e nevoie sa facem new la obiect si ajunge sa schimba doar cateva valori interne din obiect.


  1. As zice ca totusi codul face ceea ce ar trebui sa faca (in lipsa mai multor info) - cine a adaugat acolo ref, daca nu era beat, a facut-o cu scopul ca metoda sa aiba side effects, si sa poata modifica valoarea parametrilor (bad style, da' asta e alta poveste).


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 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 …

Entity Framework (EF) TransactionScope vs Database.BeginTransaction

In today blog post we will talk a little about a new feature that is available on EF6+ related to Transactions.
Until now, when we had to use transaction we used ‘TransactionScope’. It works great and I would say that is something that is now in our blood.
using (var scope = new TransactionScope(TransactionScopeOption.Required)) { using (SqlConnection conn = new SqlConnection("...")) { conn.Open(); SqlCommand sqlCommand = new SqlCommand(); sqlCommand.Connection = conn; sqlCommand.CommandText = ... sqlCommand.ExecuteNonQuery(); ... } scope.Complete(); } Starting with EF6.0 we have a new way to work with transactions. The new approach is based on Database.BeginTransaction(), Database.Rollback(), Database.Commit(). Yes, no more TransactionScope.
In the followi…