Handling out variables in C# 7.0

Most of you will be familiar with “out” variables in C#. They are often misused to return multiple values from a function and can indicate a code smell.

Nevertheless they exist and 7.0 provides some new syntax in this area.

Here’s a typical example from the well-known built-in TryParse function from before C# 7.0:

public void OldWay()
	int number;
	if (int.TryParse("1234", out number))

We instantiate “number”, pass it to TryParse and it will be populated with 1234 if the parse succeeds.

C# 7 saves us from the necessity of declaring a variable up front in the following way:

public void NewWay()
	//include out param in expression
	if (int.TryParse("1234", out int number)) //works with "var" as well as with the concrete object type

So we declare “number” in an expression and it will be available outside the “if” block as well.

If parsing fails then the declared variable will get a default value. Numbers get 0, reference types “null” etc.

View all various C# language feature related posts here.


Using delimiters for numeric literals in C# 7.0

Say you need to work with relatively large numbers in your C# code:

int number = 3452123;

Wouldn’t it be nice if you could use some kind of delimiter to indicate the millions, thousands etc? Like in 3,452,123? In C# 7.0 the underscore provides a solution for this:

int number = 3_452_123;

The underscores will be ignored by the compiler.

View all various C# language feature related posts here.

Using the ValueTask of T object in C# 7.0

By now probably all .NET developers are aware of the await and async keywords, what they do and how they work.

Here’s a small example where the CalculateSum function simulates a potentially time-consuming mathematical operation:

public class AsyncValueTaskDemo
	public void RunDemo()
		int res = CalculateSum(0, 0).Result;

	private async Task<int> CalculateSum(int a, int b)
		if (a == 0 && b == 0)
			return 0;

		return await Task.Run(() => a + b);

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