Difference in C# between different getter styles

c# getter shorthand coding-style
WoIIe picture WoIIe · Sep 5, 2017 · Viewed 10.2k times · Source

I do sometimes see abbreviations in properties for the getter. E.g. those two types:

public int Number { get; } = 0

public int Number => 0;

Can someone please tell me if there are any differences between those two. How do they behave? Are both of them read-only?

Answer

Jon Skeet picture Jon Skeet · Sep 5, 2017

Yes, both of them are read-only, but there is a difference. In the first one, there's a backing field which is initialized to 0 before the constructor is executed. You can change the value only in the constructor, just like a regular read-only field. The getter itself just returns the value of the field.

In the second one, the getter just returns 0 every time, with no field involved.

So to avoid using any automatically implemented properties or expression-bodied members at all, we have:

First version

private readonly int _number = 0;
public int Number { get { return _number; } }

Second version

public int Number { get { return 0; } }

A clearer example of the difference might be seen like this:

public DateTime CreationTime { get; } = DateTime.UtcNow;
public DateTime CurrentTime => DateTime.UtcNow;

If you create a single object, its CreationTime property will always give the same result - because it's stored in a readonly field, initialized on object construction. However, every time you access the CurrentTime property, that will cause DateTime.UtcNow to be evaluated, so you'll get a potentially different result.

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