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com.xamarin.workbook |
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Some examples from Xamarin's intro to C# 6.
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Null-conditional operator
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String Interpolation
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Expression-bodied Function Members
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Auto-property Initialization
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Index Initializers
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using static
The ?.
operator automatically does a null-check before referencing the
specified member. The example string array below has a null
entry:
var names = new string[] { "Foo", null };
In C# 5, a null-check is required before accessing the .Length
property:
// C# 5
int secondLength = 0;
if (names[1] != null)
secondLength = names[1].Length;
C# 6 allows the length to be queried in a single line; the entire
statement returns null
if any object is null.
var length0 = names[0]?.Length; // 3
var length1 = names[1]?.Length; // null
This can be used in conjunction with the ??
null coalescing operator
to set a default value (such as 0
) in the example below:
var lengths = names.Select (names => names?.Length ?? 0); //[3, 0]
Previously strings were built in a number of different ways:
var animal = "Monkeys";
var food = "bananas";
var out1 = String.Format ("{0} love to eat {1}", animal, food);
var out2 = animal + " love to eat " + food;
// or even StringBuilder
C# 6 provides a simple syntax where the fieldname can be embedded directly in the string:
$"{animal} love to eat {food}"
String-formatting can also be done with this syntax:
var values = new int[] { 1, 2, 3, 4, 12, 123456 };
foreach (var s in values.Select (i => $"The value is {i,10:N2}.")) {
Console.WriteLine (s);
}
The ToString
override in the following class is an expression-bodied
function - a more succinct declaration syntax.
class Person
{
public string FirstName { get; }
public string LastName { get; }
public Person (string firstname, string lastname)
{
FirstName = firstname;
LastName = lastname;
}
// note there is no explicit `return` keyword
public override string ToString () => $"{LastName}, {FirstName} {LastName}";
}
void
expression bodied functions are also allowed so long as
the expression is a statement:
public void Log(string message) => System.Console.WriteLine($"{DateTime.Now.ToString ("s", System.Globalization.CultureInfo.InvariantCulture )}: {message}");
This simple example calls these two methods:
Log(new Person("James", "Bond").ToString())
Properties (ie. specified with {get;set;}
) can be initialized inline
with C# 6:
class Todo
{
public bool Done { get; set; } = false;
public DateTime Created { get; } = DateTime.Now;
public string Description { get; }
public Todo (string description)
{
this.Description = description; // can assign (only in constructor!)
}
public override string ToString () => $"'{Description}' was created on {Created}";
}
new Todo("buy apples")
Dictionary-style data structures let you specify key/value types with a simple object-initializer-like syntax:
var userInfo = new Dictionary<string,object> {
["Created"] = DateTime.Now,
["Due"] = DateTime.Now.AddSeconds(60 * 60 * 24),
["Task"] = "buy lettuce"
};
Enumerations, and certain classes such as System.Math, are primarily holders of static values and functions. In C# 6, you can import all static members of a type with a single using static statement:
using static System.Math;
C# 6 code can then reference the static members directly, avoiding
repetition of the class name (eg. Math.PI
becomes PI
):
public class Location
{
public Location (double lat, double @long) {Latitude = lat; Longitude = @long;}
public double Latitude = 0; public double Longitude = 0;
}
static public double MilesBetween(Location loc1, Location loc2)
{
double rlat1 = PI * loc1.Latitude / 180;
double rlat2 = PI * loc2.Latitude / 180;
double theta = loc1.Longitude - loc2.Longitude;
double rtheta = PI * theta / 180;
double dist =
Sin(rlat1) * Sin(rlat2) + Cos(rlat1) *
Cos(rlat2) * Cos(rtheta);
dist = Acos(dist);
dist = dist*180/PI;
dist = dist*60*1.1515;
return dist; //miles
}
MilesBetween (new Location(-12,22), new Location(-13,33))