Csharp70Features.cs

//--------------------------------------------------------------------------------------
// C# 7.0 Features - Các tính năng nổi bật trên phiên bản C# 7.0  
//--------------------------------------------------------------------------------------

//--------------------------------------------------------------------------------------
// 1. Out varibales   
//--------------------------------------------------------------------------------------

//--------------------------------------------------------------------------------------
// Các phiên bản trước
int result;
if (int.TryParse(input, out result))
    Console.WriteLine(result);

//--------------------------------------------------------------------------------------
// C# 7 cho phép khai báo biến out trực tiếp trong hàm
if (int.TryParse(input, out int result))
    Console.WriteLine(result);

//--------------------------------------------------------------------------------------
// 2. Tuples   
//--------------------------------------------------------------------------------------

//--------------------------------------------------------------------------------------
// Việc khai báo tuple giờ đã linh hoạt và tường minh hơn
(string Alpha, string Beta) namedLetters = ("a", "b");
Console.WriteLine($"{namedLetters.Alpha}, {namedLetters.Beta}");
var alphabetStart = (Alpha: "a", Beta: "b");
Console.WriteLine($"{alphabetStart.Alpha}, {alphabetStart.Beta}");
(int max, int min) = Range(numbers);
Console.WriteLine(max);
Console.WriteLine(min);


//--------------------------------------------------------------------------------------
// 3. Discards : Sử dụng ký tự _ cho các trường hợp mà ta không quan tâm
//--------------------------------------------------------------------------------------

private static (string, double, int, int, int, int) QueryCityDataForYears(string name, int year1, int year2)
{
    int population1 = 0, population2 = 0;
    double area = 0;
    
    if (name == "New York City") {
        area = 468.48; 
        if (year1 == 1960) {
        population1 = 7781984;
        }
        if (year2 == 2010) {
        population2 = 8175133;
        }
    return (name, area, year1, population1, year2, population2);
    }

    return ("", 0, 0, 0, 0, 0);
}
var (_, _, _, pop1, _, pop2) = QueryCityDataForYears("New York City", 1960, 2010);

//--------------------------------------------------------------------------------------
// 

//--------------------------------------------------------------------------------------
// 4. Pattern matching   
//--------------------------------------------------------------------------------------

//--------------------------------------------------------------------------------------
// is operator 
if (input is int count)
    sum += count;

//--------------------------------------------------------------------------------------
// switch
public static int SumPositiveNumbers(IEnumerable<object> sequence)
{
    int sum = 0;
    foreach (var i in sequence)
    {
        switch (i)
        {
            case 0:
                break;
            case IEnumerable<int> childSequence:
            {
                foreach(var item in childSequence)
                    sum += (item > 0) ? item : 0;
                break;
            }
            case int n when n > 0:
                sum += n;
                break;
            case null:
                throw new NullReferenceException("Null found in sequence");
            default:
                throw new InvalidOperationException("Unrecognized type");
        }
    }
    return sum;
}

//--------------------------------------------------------------------------------------
// 5. Ref locals and returns   
//--------------------------------------------------------------------------------------

public static ref int Find(int[,] matrix, Func<int, bool> predicate)
{
    for (int i = 0; i < matrix.GetLength(0); i++)
        for (int j = 0; j < matrix.GetLength(1); j++)
            if (predicate(matrix[i, j]))
                return ref matrix[i, j];
    throw new InvalidOperationException("Not found");
}
ref var item = ref MatrixSearch.Find(matrix, (val) => val == 42);
Console.WriteLine(item);
item = 24;
Console.WriteLine(matrix[4, 2]);

//--------------------------------------------------------------------------------------
// 6. Local functions   
//--------------------------------------------------------------------------------------

public Task<string> PerformLongRunningWork(string address, int index, string name)
{
    if (string.IsNullOrWhiteSpace(address))
        throw new ArgumentException(message: "An address is required", paramName: nameof(address));
    if (index < 0)
        throw new ArgumentOutOfRangeException(paramName: nameof(index), message: "The index must be non-negative");
    if (string.IsNullOrWhiteSpace(name))
        throw new ArgumentException(message: "You must supply a name", paramName: nameof(name));

    return longRunningWorkImplementation();

    async Task<string> longRunningWorkImplementation()
    {
        var interimResult = await FirstWork(address);
        var secondResult = await SecondStep(index, name);
        return $"The results are {interimResult} and {secondResult}. Enjoy.";
    }
}

//--------------------------------------------------------------------------------------
// 7. More expression-bodied members   
//--------------------------------------------------------------------------------------

// Expression-bodied constructor
public ExpressionMembersExample(string label) => this.Label = label;

// Expression-bodied finalizer
~ExpressionMembersExample() => Console.Error.WriteLine("Finalized!");

private string label;

// Expression-bodied get / set accessors.
public string Label
{
    get => label;
    set => this.label = value ?? "Default label";
}

//--------------------------------------------------------------------------------------
// 8. Throw expressions   
//--------------------------------------------------------------------------------------

public string Name
{
    get => name;
    set => name = value ?? 
        throw new ArgumentNullException(paramName: nameof(value), message: "Name cannot be null");
}  
DateTime ToDateTime(IFormatProvider provider) => 
         throw new InvalidCastException("Conversion to a DateTime is not supported.");

//--------------------------------------------------------------------------------------
// 9. Generalized async return types 
//--------------------------------------------------------------------------------------

public async ValueTask<int> Func()
{
    await Task.Delay(100);
    return 5;
}

//--------------------------------------------------------------------------------------
// 10. Numeric literal syntax improvements  
//--------------------------------------------------------------------------------------

public const int Sixteen =   0b0001_0000;
public const int ThirtyTwo = 0b0010_0000;
public const int SixtyFour = 0b0100_0000;
public const int OneHundredTwentyEight = 0b1000_0000;
public const long BillionsAndBillions = 100_000_000_000;
public const double AvogadroConstant = 6.022_140_857_747_474e23;
public const decimal GoldenRatio = 1.618_033_988_749_894_848_204_586_834_365_638_117_720_309_179M;