c#开发者应该了解的15个特性 浅谈c#开发者应该了解的15个特性

public static class ObsoleteExample
{
    // Mark OrderDetailTotal As Obsolete.
    [ObsoleteAttribute("This property (DepricatedOrderDetailTotal) is obsolete. 
                       Use InvoiceTotal instead.", false)]
    public static decimal OrderDetailTotal
    {
        get
        {
            return 12m;
        }
    }

    public static decimal InvoiceTotal
    {
        get
        {
            return 25m;
        }
    }

    // Mark CalculateOrderDetailTotal As Obsolete.
    [ObsoleteAttribute("This method is obsolete. Call CalculateInvoiceTotal instead.", true)]
    public static decimal CalculateOrderDetailTotal()
    {
        return 0m;
    }

    public static decimal CalculateInvoiceTotal()
    {
        return 1m;
    }
}

Console.WriteLine(ObsoleteExample.OrderDetailTotal);
Console.WriteLine( );
Console.WriteLine(ObsoleteExample.CalculateOrderDetailTotal());

public class DefaultValueAttributeTest
{
    public DefaultValueAttributeTest()
    {
        // Use the DefaultValue property of each property to actually set it, via reflection.
        foreach (PropertyDescriptor prop in TypeDescriptor.GetProperties(this))
        {
            DefaultValueAttribute attr = (DefaultValueAttribute)prop.Attributes
                                         [typeof(DefaultValueAttribute)];
            if (attr != null)
            {
                prop.SetValue(this, attr.Value);
            }
        }
    }

    [DefaultValue(25)]
    public int Age { get; set; }

    [DefaultValue("Anton")]
    public string FirstName { get; set; }

    [DefaultValue("Angelov")]
    public string LastName { get; set; }

    public override string ToString()
    {
        return string.Format("{0} {1} is {2}.", this.FirstName, this.LastName, this.Age);
    }
}

public static class DebuggerBrowsableTest
{
    private static string squirrelFirstNameName;
    private static string squirrelLastNameName;

    // The following DebuggerBrowsableAttribute prevents the property following it 
    // from appearing in the debug window for the class.
    [DebuggerBrowsable(DebuggerBrowsableState.Never)]
    public static string SquirrelFirstNameName 
    {
        get
        {
            return squirrelFirstNameName;
        }
        set
        {
            squirrelFirstNameName = value;
        }
    }

    [DebuggerBrowsable(DebuggerBrowsableState.Collapsed)]
    public static string SquirrelLastNameName
    {
        get
        {
            return squirrelLastNameName;
        }
        set
        {
            squirrelLastNameName = value;
        }
    }
}

int? x = null;
int y = x ?? -1;
Console.WriteLine("y now equals -1 because x was null => {0}", y);
int i = DefaultValueOperatorTest.GetNullableInt() ?? default(int);
Console.WriteLine("i equals now 0 because GetNullableInt() returned null => {0}", i);
string s = DefaultValueOperatorTest.GetStringValue();
Console.WriteLine("Returns 'Unspecified' because s is null => {0}", s ?? "Unspecified");

public static class CurryMethodExtensions
{
    public static Func<A, Func<B, Func<C, R>>> Curry<A, B, C, R>(this Func<A, B, C, R> f)
    {
        return a => b => c => f(a, b, c);
    }
}
Func<int, int, int, int> addNumbers = (x, y, z) => x + y + z;
var f1 = addNumbers.Curry();
Func<int, Func<int, int>> f2 = f1(3);
Func<int, int> f3 = f2(4);
Console.WriteLine(f3(5));

public static class CurryMethodExtensions
{
    public static Func<C, R> Partial<A, B, C, R>(this Func<A, B, C, R> f, A a, B b)
    {
        return c => f(a, b, c);
    }
}

Func<int, int, int, int> sumNumbers = (x, y, z) => x + y + z;
Func<int, int> f4 = sumNumbers.Partial(3, 4);
Console.WriteLine(f4(5));

WeakReferenceTest hugeObject = new WeakReferenceTest();
hugeObject.SharkFirstName = "Sharky";
WeakReference w = new WeakReference(hugeObject);
hugeObject = null;
GC.Collect();
Console.WriteLine((w.Target as WeakReferenceTest).SharkFirstName);

public abstract class ThreadSafeLazyBaseSingleton<T>
    where T : new()
{
    private static readonly Lazy<T> lazy = new Lazy<T>(() => new T());
    
    public static T Instance
    {
        get
        {
            return lazy.Value;
        }
    }
}

string positiveString = "91389681247993671255432112000000";
string negativeString = "-90315837410896312071002088037140000";
BigInteger posBigInt = 0;
BigInteger negBigInt = 0;

posBigInt = BigInteger.Parse(positiveString);
Console.WriteLine(posBigInt);
negBigInt = BigInteger.Parse(negativeString);
Console.WriteLine(negBigInt);

int i = 21;
TypedReference tr = __makeref(i);
Type t = __reftype(tr);
Console.WriteLine(t.ToString());
int rv = __refvalue( tr,int);
Console.WriteLine(rv);
ArglistTest.DisplayNumbersOnConsole(__arglist(1, 2, 3, 5, 6));

public static class ArglistTest
{
    public static void DisplayNumbersOnConsole(__arglist)
    {
        ArgIterator ai = new ArgIterator(__arglist);
        while (ai.GetRemainingCount() > 0)
        {
            TypedReference tr = ai.GetNextArg();
            Console.WriteLine(TypedReference.ToObject(tr));
        }
    }
}

Console.WriteLine("NewLine: {0}  first line{0}  second line{0}  third line", Environment.NewLine);

ExceptionDispatchInfo possibleException = null;
try
{
    int.Parse("a");
}
catch (FormatException ex)
{
    possibleException = ExceptionDispatchInfo.Capture(ex);
}

if (possibleException != null)
{
    possibleException.Throw();
}

string s = Console.ReadLine();
try
{
    int i = int.Parse(s);
    if (i == 42) Environment.FailFast("Special number entered");
}
finally
{
    Console.WriteLine("Program complete.");
}

Debug.Assert(1 == 0, "The numbers are not equal! Oh my god!");

Debug.WriteLineIf(1 == 1, "This message is going to be displayed in the Debug output! =)");

Debug.WriteLine("What are ingredients to bake a cake?");
Debug.Indent();
Debug.WriteLine("1. 1 cup (2 sticks) butter, at room temperature.");
Debug.WriteLine("2 cups sugar");
Debug.WriteLine("3 cups sifted self-rising flour");
Debug.WriteLine("4 eggs");
Debug.WriteLine("1 cup milk");
Debug.WriteLine("1 teaspoon pure vanilla extract");
Debug.Unindent();
Debug.WriteLine("End of list");

int[] nums = Enumerable.Range(0, 1000000).ToArray();
long total = 0;

// Use type parameter to make subtotal a long, not an int
Parallel.For<long>(0, nums.Length, () => 0, (j, loop, subtotal) =>
{
    subtotal += nums[j];
    return subtotal;
},
    (x) => Interlocked.Add(ref total, x)
);

Console.WriteLine("The total is {0:N0}", total);

int[] nums = Enumerable.Range(0, 1000000).ToArray();
long total = 0;

Parallel.ForEach<int, long>(nums, // source collection
                            () => 0, // method to initialize the local variable
    (j, loop, subtotal) => // method invoked by the loop on each iteration
    {
        subtotal += j; //modify local variable 
        return subtotal; // value to be passed to next iteration
    },
    // Method to be executed when each partition has completed. 
    // finalResult is the final value of subtotal for a particular partition.
(finalResult) => Interlocked.Add(ref total, finalResult));

Console.WriteLine("The total from Parallel.ForEach is {0:N0}", total);

Console.WriteLine("IsInfinity(3.0 / 0) == {0}.", Double.IsInfinity(3.0 / 0) ? "true" : "false");