Tuples and unpacking assignment support in C#?

Question

In Python I can write

def myMethod():
    #some work to find the row and col
    return (row, col)

row, col = myMethod()
mylist[row][col] # do work on this element

But in C# I find myself writing out

int[] MyMethod()
{
    // some work to find row and col
    return new int[] { row, col }
}

int[] coords = MyMethod();
mylist[coords[0]][coords[1]] //do work on this element

The Pythonic way is obivously much cleaner. Is there a way to do this in C#?

Solution 1

There's a set of Tuple classes in .NET:

Tuple<int, int> MyMethod()
{
    // some work to find row and col
    return Tuple.Create(row, col);
}

But there's no compact syntax for unpacking them like in Python:

Tuple<int, int> coords = MyMethod();
mylist[coords.Item1][coords.Item2] //do work on this element

Solution 2

For .NET 4.7 and later, you can pack and unpack a ValueTuple:

(int, int) MyMethod()
{
    return (row, col);
}

(int row, int col) = MyMethod();
// mylist[row][col]

For .NET 4.6.2 and earlier, you should install System.ValueTuple:

PM> Install-Package System.ValueTuple

Solution 3

An extension might get it closer to Python tuple unpacking, not more efficient but more readable (and Pythonic):

public class Extensions
{
  public static void UnpackTo<T1, T2>(this Tuple<T1, T2> t, out T1 v1, out T2 v2)
  {
    v1 = t.Item1;
    v2 = t.Item2;
  }
}

Tuple<int, int> MyMethod() 
{
   // some work to find row and col
   return Tuple.Create(row, col);
}

int row, col;    
MyMethod().UnpackTo(out row, out col);
mylist[row][col]; // do work on this element

Solution 4

Here is a zip example with value unpacking. Here zip returns an iterator over tuples.

int[] numbers = {1, 2, 3, 4};
string[] words = {"one", "two", "three"};

foreach ((var n, var w) in numbers.Zip(words, Tuple.Create))
{
    Console.WriteLine("{0} -> {1}", n, w);
}

Output:

1 -> one
2 -> two
3 -> three

Solution 5

C# is a strongly-typed language with a type system that enforces a rule that functions can have either none (void) or 1 return value. C# 4.0 introduces the Tuple class:

Tuple<int, int> MyMethod()
{
    return Tuple.Create(0, 1);
}

// Usage:
var myTuple = MyMethod();
var row = myTuple.Item1;  // value of 0
var col = myTuple.Item2;  // value of 1

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Comments

[Mike Christensen]

I'd probably use out parameters for that..

[Feidex]

@MikeChristensen: The Framework Design Guidelines recommend against out parameters if they can be avoided.

[maria nabil]

@MikeChristensen I thought about out parameters, but they make me feel dirty for some reason

[Admin]

@MikeChristensen And every-time I use then I want to stab someone [with a rubber knife] for not having the concept of Option/Maybe core in .NET :-)

[Admin]

Note for causal reader: Tuple<...> is standard in .NET4+ only.

[fabspro]

Note for other readers, a 2-tuple can be created in .NET < 4 (in essence) by using a KeyValuePair instead.

[0dminnimda]

note that you can use var in this expression. (not sure which version this is possible from)