What's new in VS2017 and C# 7.0? - Out Variables

When using certain APIs, some parameters are declared as out parameters.

A good example of this is the Int32.TryParse(string, out int) method.

So let’s check the difference in invocation between C# 6.0 and C# 7.0

C# 6.0

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public void DoSomething(string parameter)
{
    int result;
    if(Int32.TryParse(parameter, out result))
    {
        Console.WriteLine($"Parameter is an int and was parsed to {result}");
    }
}

C# 7.0 (with type inference)

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public void DoSomething(string parameter)
{
    if(Int32.TryParse(parameter, out int result))
    {
        Console.WriteLine($"Parameter is an int and was parsed to {result}");
    }

    // w/ type inference
    if(Int32.TryParse(parameter, out var i))
    {
      // ....
    }
}

The difference

Now you don’t need to define the variable on a separate row. You can inline it directly and, in fact, you could just use var instead of int in the previous example since it can infer the type directly inline. This is called type inference.

It is important to note however that the variable is scoped on the method and not the if itself. So the result parameter is available in both the if and the else scope.

Are you going to use it?

When new features are introduced in a language, I like to ask people whether it’s a feature they would use.

So please leave me a comment and let me know if you are going to use inline out variables.