What is the difference between LINQ methods that start with "As" and those that start with "To"?

 LINQ is a set of extension methods for the .NET Framework that allow developers to query data from various sources using a consistent syntax.

The methods that start with "As" generally return a new sequence that is a projection of the original sequence, with each element in the new sequence being a transformation of the corresponding element in the original sequence. These methods do not perform any conversion, but rather just change the way the data is presented. For example, the AsEnumerable() method returns the input sequence as an IEnumerable<T>, regardless of its original type.

On the other hand, the methods that start with "To" perform a conversion of the input sequence to a new type or format. These methods often involve creating a new collection or data structure to store the elements of the input sequence, and as such may have a performance impact. For example, the ToList() method converts an input sequence to a List<T>, and the ToDictionary() method converts an input sequence to a Dictionary<TKey, TValue>.

Does IEnumerable.ToList() have performance impacts ?

 ToList() creates a new List object and copies all the elements from the source IEnumerable<T> into the new List. This means that it has to iterate through all the elements in the source IEnumerable<T>, which has a time complexity of O(n), where n is the number of elements in the source IEnumerable<T>.

This can have a performance impact, especially if the source IEnumerable<T> is large and the operation is being performed frequently. In these cases, it may be more efficient to use a different approach, such as using a loop to add the elements to the List manually, or using a different data structure that allows for more efficient insertion and retrieval of elements.

However, in many cases the performance impact of ToList() will not be significant, especially if the source IEnumerable<T> is small or the operation is only being performed infrequently. It is generally a good idea to use ToList() when you need to work with a List rather than an IEnumerable<T>, as it can make the code more readable and easier to work with.

List Capacity vs Count

 That's correct! In the .NET framework, the List<T> class is implemented as an array that grows dynamically as items are added to it. The Capacity property represents the size of the underlying array, and the Count property represents the number of items that have been added to the list.

When you add an item to the list and the list is already at capacity, the List<T> class will automatically double the size of the underlying array and copy all of the items from the old array to the new one. This process is known as "resizing the array."

It's important to note that the Capacity property is not the same as the Count property. The Capacity property represents the size of the underlying array, while the Count property represents the number of items that have been added to the list. The Count property will always be less than or equal to the Capacity property.

For example, if you have a list with a capacity of 10 and you add 5 items to it, the Count property will be 5 and the Capacity property will be 10. If you then add another item to the list, the list will automatically resize the array and the Capacity property will be increased to 20. However, the Count property will still be 6.

Dependency Injection (DI)

The Dependency Injection pattern is a particular implementation of Inversion of Control. Inversion of Control (IoC) means that objects do not create other objects on which they rely to do their work. Instead, they get the objects that they need from an outside source (for example, an xml configuration file).



Dependency Injection (DI) means that this is done without the object intervention, usually by a framework component that passes constructor parameters and set properties.



The advantages of using Dependency Injection pattern and Inversion of Control are the following:

• Reduces class coupling
• Increases code reusing
• Improves code maintainability
• Improves application testing
  
  The principle say that "High level module should not depend upon the low level module, both should depend on abstraction. Details should depends upon abstraction". 
  
  
  

  Basically, instead of having your objects creating a dependency or asking a factory object to make one for them, you pass the needed dependencies in to the constructor or via property setters, and you make it somebody else's problem (an object further up the dependency graph, or a dependency injector that builds the dependency graph). A dependency as I'm using it here is any other object the current object needs to hold a reference to. One of the major advantages of dependency injection is that it can make testing lots easier. Suppose you have an object which in its constructor does something like: public SomeClass() { myObject = Factory.getObject(); } This can be troublesome when all you want to do is run some unit tests on SomeClass, especially if myObject is something that does complex disk or network access. So now you're looking at mocking myObject but also somehow intercepting the factory call. Hard. Instead, pass the object in as an argument to the constructor. Now you've moved the problem elsewhere, but testing can become lots easier. Just make a dummy myObject and pass that in. The constructor would now look a bit like: public SomeClass (MyClass myObject) { this.myObject = myObject; }

C# DateTime from Excel turns into float number

 In Excel, dates and times are stored as a floating point number representing the number of days since the epoch date of January 1, 1970. This means that when you read a date or time value from an Excel file into a C# DateTime object, you will need to convert the floating point value to a DateTime object.

Here is an example of how you could do this in C#:

// Assume that the Excel date value is stored in a variable called "excelDate" // Convert the Excel date value to a DateTime object DateTime dateTime = DateTime.FromOADate(excelDate); // You can also use the following syntax to achieve the same result: // DateTime dateTime = new DateTime((long)(excelDate * 86400000) + new DateTime(1970, 1, 1).Ticks);

In this example, the FromOADate method is used to convert the Excel date value to a DateTime object. This method is part of the System.DateTime struct and takes a floating point value representing the number of days since the epoch date.

Alternatively, you can use the Ticks property of the DateTime struct and some simple math to convert the Excel date value to a DateTime object. In this case, the value is first converted to a number of ticks (multiplying it by the number of ticks per day), and then the resulting ticks are

How to make sure unmanaged memory release .net core ?

 In .NET Core, unmanaged memory is typically allocated and released through the use of pointers and the Marshal.AllocHGlobal and Marshal.FreeHGlobal methods. These methods are part of the System.Runtime.InteropServices namespace and are used to allocate and release unmanaged memory in the global heap.

To ensure that unmanaged memory is properly released, you should make sure to call the FreeHGlobal method when you are finished using the memory. You can do this in a finally block to ensure that the memory is released even if an exception is thrown. Here is an example of how you might use these methods to allocate and release unmanaged memory in .NET Core:

using System; using System.Runtime.InteropServices; namespace UnmanagedMemoryExample { class Program { static void Main(string[] args) { // Allocate unmanaged memory IntPtr ptr = Marshal.AllocHGlobal(1024); try { // Use the unmanaged memory here... } finally { // Release the unmanaged memory Marshal.FreeHGlobal(ptr); } } } }

Note that you should only use the global heap for small blocks of memory that are needed for a short period of time. For larger blocks of memory or for memory that is needed for a longer period of time, you should consider using the Marshal.AllocCoTaskMem method or creating a managed wrapper class that can be used to manage the memory.

It is also a good idea to use the using statement whenever possible to automatically release resources when they are no longer needed. This can help simplify your code and reduce the chances of resource leaks.

linq query to get maximum salary in employee list object

 Here is an example of how you could use LINQ (Language Integrated Query) to get the maximum salary in a list of employee objects in C#:

  using System.Linq;

// Assume that the list of employees is stored in a variable called "employees"

// Get the maximum salary from the list of employees

decimal maxSalary = employees.Max(e => e.Salary);

// You can also use the following syntax to achieve the same result:

// decimal maxSalary = (from e in employees select e.Salary).Max();

In this example, the Max method is used to get the maximum salary from the list of employees. The method takes a lambda expression that specifies the property to use for the comparison (in this case, the Salary property).

Alternatively, you can use a LINQ query to achieve the same result. The query uses the from and select clauses to specify the source collection and the property to select, and the Max method is used to get the maximum value.

Note that this code assumes that the employees list and the Employee class have already been defined and that the Employee class has a Salary property of type decimal. You will need to modify the code to match the structure of your own data.