This is part of a series of articles on new features introduced in C# 9.
C# 9 introduced some enhancements to reduce the amount of code you need when creating new instances of objects.These target-typed new expressions “Do not require type specification for constructors when the type is known.” [MS]
As an example in C# 8 with fields you need to explicitly create an instance:
1 2 3 4 | class Preferences
{
private List<string> _favoriteColors = new List<string>();
}
|
From C# 9 you can instead write:
1 2 3 4 | class Preferences
{
private List<string> _favoriteColors = new();
}
|
Notice in the preceding code you can simply write new() because the target type is known to be List<string>.
If you are calling a method (or constructor) that requires an instance of an object, you can also use new(). For example suppose you had the following method that requires a DisplayOptions instance:
1 2 3 4 5 6 7 8 | public void DisplayColors(DisplayOptions options)
{
Console.WriteLine(options.Title);
foreach (var color in _favoriteColors)
{
Console.WriteLine(color);
}
}
|
Prior to C# 9, if you wanted to just create a new instance of DisplayOptions and pass it in you would write:
1 2 | var prefs = new Preferences();
prefs.DisplayColors(new DisplayOptions());
|
With C# 9 you can simplify this to:
1 2 | var prefs = new Preferences();
prefs.DisplayColors(new());
|
You could also write this using a target-typed new expression for the Preferences instance:
1 2 | Preferences prefs = new();
prefs.DisplayColors(new());
|
If you have init only properties you can also use target-typed new expressions:
1 2 3 4 | class DisplayOptions
{
public string Title { get; init; }
}
|
1 | DisplayOptions options = new() { Title = "Colors" };
|
If you want to fill in the gaps in your C# knowledge be sure to check out my C# Tips and Traps training course from Pluralsight – get started with a free trial.
SHARE: