Generic Method with Unknown Number of Dimensions

Nathan Sokalski 4,126

I have a Generic Method in which the return type will be a Jagged Array. However, the number of dimensions is unknown at design time (the return type could end up being T[], T[][], T[][][], or even T[][][][][][][][][]). It would be very inefficient to create an overload for all scenarios. Is there a way to dynamically specify the number of dimensions in the return type?

Viorel 114.7K Reputation points

2022-09-25T14:49:30.127+00:00

Maybe your function should return an object, object [ ], dynamic, or Array? The callers will cast the result to the expected array type.

2 answers

Bruce (SqlWork.com) 61,731 Reputation points

2022-09-25T15:39:57.367+00:00

No, you need an overload for each. MS ran into the same issue with Tuple<>, and needed to keep making it more overloads. c# would need a macro system like rust to be able to do this.

As suggested you need all the overloads, or use an object.and cast the method results or use dynamic.
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Nathan Sokalski 4,126 Reputation points

2022-09-25T17:15:50.943+00:00

Using Object and casting the result did not seem to work. Here is the code I am trying to use:

public static Object CreateJaggedArray<T>(int[] dimensions) { if (dimensions.Length == 0) { return null; } else { object current = new T[dimensions[^1]]; for (int i = (dimensions.Length - 2); i >= 0; i--) { current = Enumerable.Repeat(current, dimensions[i]).ToArray(); } return current; } }

However, with this code the current variable is always Object[] (after initialization, at the beginning & end of all iterations of the for loop, and when being returned). I would expect it to increase the number of dimensions with each iteration (Object[], Object[][], Object[][][], etc.). The following statically typed code works fine:

public static T[][][][] CreateJagged4<T>(int[] dimensions) { return Enumerable.Repeat( Enumerable.Repeat( Enumerable.Repeat(new T[dimensions[3]], dimensions[2]).ToArray() , dimensions[1]).ToArray() , dimensions[0]).ToArray(); }

This code is obviously not complicated, and the overloads are not hard to make, but it still requires making them. But the overloads would require specifying the dimensions as multiple parameters (or a different name, which would make them not actually overloads) since they would otherwise all have the same parameter of int[] dimensions.
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Viorel 114.7K Reputation points

2022-09-25T18:24:26.82+00:00
If the question is how to write the function, then try an approach:

static object CreateJagged<T>( int[] dimensions ) { if( dimensions.Length == 1 ) { return new T[dimensions[0]]; } else { return Enumerable.Repeat( CreateJagged<T>( dimensions.Skip( 1 ).ToArray( ) ), dimensions[0] ).ToArray( ); } }
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Nathan Sokalski 4,126 Reputation points

2022-09-25T19:06:55.807+00:00

That is probably a better way to write the function, but it still does something that mine did that needs fixed. At each iteration (or recursive call like yours) the result is still Object[]. This is causing the following Exception when attempting to cast. For example (and I tried this with both my code and yours), when I call the method as follows:

float[][][][] xxx = (float[][][][])ArrayExtensions.CreateJaggedArray<float>(new[] { 1, 13, 13, 85 });

It gives the following:

System.InvalidCastException: Specified cast is not valid.

Is there a way to allow it to be cast?
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Generic Method with Unknown Number of Dimensions

2 answers