Skip to main content

Delegates from .NET 1.0 to .NET 4.0

Mai mult ca sigur ati folosit delegate. Sunt utili cand trebuie sa specificam un comportament la runtime si nu la compile time. Prin acest mecanism putem sa scapam de mostenire in locurile unde aceasta a fost folosita pentru a definii un comportament specific.
Exista mai multe tipuri de delegates definite core-ul de .NET:
  • Predicate
  • Action
  • Func
O sa incerc sa descriu pe scurt fiecare tip de delegate:
Action reprezinta o actiune care nu returneaza nici un rezultat. Header-ul la metoda ar fi de forma urmatoare
void fx(T)
Exista mai multe implementari de Action, se pot definii pana la maxim 16 parametrii. In cazul in care avem nevoie de mai mult de 16 parametri, ne putem definii noi propile actiuni, dar nu cred ca este sanatos sa avem o actiune cu 16 parametrii sau mai multi.
Predicate reprezinta o conditie care se ruleaza si care returneaza TRUE sau FALSE
bool fx(T)
Atat Action cat si Predicate apar odata cu .NET 2.0, dar ajung sa fie folosite la adevarata lor valoare abia in .NET 3.5 cand apare si Func impreuna cu expresiile lambda.
Func<T1...,TResult> specifica un delegate care accepta de la 0 la 16 parametrii si returneaza un rezultat de tipul TResult. Este bine de retinut faptul ca tipul rezultatului este definit mereu ca si ultimul parametru.
TResult fx(T1,...)
Acuma ca stim ce reprezinta fiecare din ele, ar fi interesant sa vedem cum au aparut si evoluat in timp.
In .NET 1.0 si .NET 1.1 daca aveai nevoie de un delegate era nevoie sa iti declari un delegate de forma:
delegate bool GetHalfDelegate(int number);
Urmatorul pas era declari o metoda care are aceiasi semnatura cu delegatul pe care l-ai declarat si apoi sa instantiezi o variabila de tipul respectiv.

public bool GetHalf(int number) { ... }
...
GetHalfDelegate getHalf = new GetHalfDelegate(this.GetHalf);
Pentru a putea apela acest delegate era nevoie de un apel de forma:
int result = getHalf(97);
Odata cu aparitia la .NET 2.0 apare si conceptul de metode anonime. Prin acest mecanism putem sa ne definim o logica fara a scrie o metoda. In cazul nostru nu mai este nevoie sa ne definim medoda GetHalf, ajunge doar ca in momentul in care instantiem variabila getHalf sa scriem codul care vrem sa se execute.
GetHalfDelegate getHalf = delegate(int number)
{
return number/2;
};
Lucruriile se simplifica umpic, dar cu .NET 3.5 totul ajunge mult mai simplu. Putem sa ne folosim de Func. Orice metoda definita cu acest antet o sa poata sa fie folosita. Cel care defineste metoda nu va mai avea nevoie sa aibe o referinta la tipul delegat-ului Tot ce mai este nevoie sa scriem este:
Func<int,int> getHalf = (number) => number/2;
Mi s-a parut destul de interesant modul in care sintaxa a evoluat de la 1.0 la 3.5.
In .NET 4.0 nu a mai aparut nimic special la acest nivel, dar cu ajutorul lui var putem sa rescriem codul sub forma
var getHalf = (number) => number/2;
Trebuie avut grija cat de mult folosim aceste elemente. Viteza de executie a codului poate sa scada in care face exces, iar nu in ultimul rand codul scris poate sa fie mult mai greu de inteles.

Comments

Popular posts from this blog

Windows Docker Containers can make WIN32 API calls, use COM and ASP.NET WebForms

After the last post , I received two interesting questions related to Docker and Windows. People were interested if we do Win32 API calls from a Docker container and if there is support for COM. WIN32 Support To test calls to WIN32 API, let’s try to populate SYSTEM_INFO class. [StructLayout(LayoutKind.Sequential)] public struct SYSTEM_INFO { public uint dwOemId; public uint dwPageSize; public uint lpMinimumApplicationAddress; public uint lpMaximumApplicationAddress; public uint dwActiveProcessorMask; public uint dwNumberOfProcessors; public uint dwProcessorType; public uint dwAllocationGranularity; public uint dwProcessorLevel; public uint dwProcessorRevision; } ... [DllImport("kernel32")] static extern void GetSystemInfo(ref SYSTEM_INFO pSI); ... SYSTEM_INFO pSI = new SYSTEM_INFO(

Azure AD and AWS Cognito side-by-side

In the last few weeks, I was involved in multiple opportunities on Microsoft Azure and Amazon, where we had to analyse AWS Cognito, Azure AD and other solutions that are available on the market. I decided to consolidate in one post all features and differences that I identified for both of them that we should need to take into account. Take into account that Azure AD is an identity and access management services well integrated with Microsoft stack. In comparison, AWS Cognito is just a user sign-up, sign-in and access control and nothing more. The focus is not on the main features, is more on small things that can make a difference when you want to decide where we want to store and manage our users.  This information might be useful in the future when we need to decide where we want to keep and manage our users.  Feature Azure AD (B2C, B2C) AWS Cognito Access token lifetime Default 1h – the value is configurable 1h – cannot be modified

What to do when you hit the throughput limits of Azure Storage (Blobs)

In this post we will talk about how we can detect when we hit a throughput limit of Azure Storage and what we can do in that moment. Context If we take a look on Scalability Targets of Azure Storage ( https://azure.microsoft.com/en-us/documentation/articles/storage-scalability-targets/ ) we will observe that the limits are prety high. But, based on our business logic we can end up at this limits. If you create a system that is hitted by a high number of device, you can hit easily the total number of requests rate that can be done on a Storage Account. This limits on Azure is 20.000 IOPS (entities or messages per second) where (and this is very important) the size of the request is 1KB. Normally, if you make a load tests where 20.000 clients will hit different blobs storages from the same Azure Storage Account, this limits can be reached. How we can detect this problem? From client, we can detect that this limits was reached based on the HTTP error code that is returned by HTTP