Back to C# basics: Difference between "=>" and "{ get; } =" for properties

11 Nov 2020 1 mins .NET

I recently realized, the difference between => and { get; } = for properties might not be as known as everybody thinks, based on code I saw multiple times.

Here’s an example code.

public class C
{
	public Foo A { get; } = new Foo();
	public Foo B => new Foo();
}

Is it the same or is it not? The answer is, it’s not the same. The A property is property with getter only (aka read only or immutable property). When C instance is created a new instance of Foo is assigned to the property and will be returned from now on. The B property defines also only getter, but this time the getter contains the new Foo(); as it’s body, aka returning new instance of Foo every time you access B.

Putting it into barebone C#, it would look like this.

public class C
{
	readonly Foo _a = new Foo();
	
	public Foo A
	{
		get { return _a; }
	}

	public Foo B
	{
		get { return new Foo(); }
	}
}

Makes sense?

Jiří Činčura is .NET, C# and Firebird expert. He focuses on data and business layers, language constructs, parallelism, databases and performance. For almost two decades he contributes to open-source, i.e. FirebirdClient. He works as a senior software engineer for Microsoft. Frequent speaker and blogger at www.tabsoverspaces.com.