Prior to this feature the using directive could create an alias for any named type.

C# 12 enables the using directive to create aliases for un-named types like tuples, pointer types etc.

Code

Now

using GeoCoordinate = (double latitude, double longitude);

GeoCoordinate location = GetLocation();
PrintLocation(location);

void PrintLocation(GeoCoordinate loc)
  => Console.WriteLine($"Latitude: {loc.latitude}, Longitude: {loc.longitude}");

GeoCoordinate GetLocation() => new(1.1, 2.2);

Before

// Remember (double latitude, double longitude) is a Geolocation

(double latitude, double longitude) location = GetLocation();
PrintLocation(location);

void PrintLocation((double latitude, double longitude) loc)
    => Console.WriteLine($"Latitude: {loc.latitude}, Longitude: {loc.longitude}");

(double, double) GetLocation() => new(1.1, 2.2);

Before (alternative)

GeoCoordinate location = GetLocation();
PrintLocation(location);

void PrintLocation(GeoCoordinate loc)
    => Console.WriteLine($"Latitude: {loc.latitude}, Longitude: {loc.longitude}");

GeoCoordinate GetLocation() => new(1.1, 2.2);

record GeoCoordinate
{
    public double latitude { get; init; }
    public double longitude { get; init; }

    public GeoCoordinate(double latitude, double longitude)
    {
      this.latitude = latitude;
      this.longitude = longitude;
    }
}

Notes

• Works with tuples, pointer types, array types, and other types that previously could not be aliased
• The alias is scoped to the file, just like a regular using directive
• Combine with global using directives ^{C# 10.0} to share aliases across your project

More information

• What's new in C# 12.0
• Proposal