How to have empty array as part of implict array in C#

Question

This declaration causes an error because the last item is empty.

  var foo = new[] {
                 new [] {1, 2, 3},
                 new [] {3, 4, 5},
                 new [] {}
                 };

I understand that in general the compiler would need all these arrays to be of the same (anonymous) type, but it seems like it should allow "empty" as a special case and type it like all the others.

Is there some way to declare the above so that I can have an empty array along with the non-empty ones?

Michael

It cannot determine the Type of the elements. (because it has no elements) — Dennis_E, Mar 21 '16 at 14:46

Dennis_E · Answer 1 · 2016-03-21T14:54:05.293

7

new [] {1, 2, 3}

is shorthand for

new int[] { 1,2,3 }

The compiler can figure out it has to be int because the array contains ints.
But if you say

new [] { }

since the array is empty, the Type cannot be determined. So you have to explicitly tell the compiler what the Type is:

var foo = new[] {
             new [] {1, 2, 3},
             new [] {3, 4, 5},
             new int [] {}
             };

edited Mar 21 '16 at 14:54

answered Mar 21 '16 at 14:49

Dennis_E

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score 5 · Answer 2 · answered Mar 21 '16 at 14:45

5

Sure, just make it an int[]:

int[][] foo = new[] {
         new [] {1, 2, 3},
         new [] {3, 4, 5},
         new int[] {}
};

answered Mar 21 '16 at 14:45

Tim Schmelter

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James Dev · Answer 3 · 2016-03-21T14:50:30.977

0

You can if you iniltialise to a specific type:

        var foo = new int[][] {
             new int[] {1, 2, 3},
             new int[] {3, 4, 5},
             new int[] {}
             };

edited Mar 21 '16 at 14:50

answered Mar 21 '16 at 14:47

James Dev

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16

Where is the cast? – Tim Schmelter Mar 21 '16 at 14:49

score 0 · Answer 4 · edited May 23 '17 at 12:31

0

Creating an empty array implicitly is not possible. As @Dennis_E said "since the array is empty, the Type cannot be determined. "

You can refer to All possible C# array initialization syntaxes

Quoting from related part:

Empty arrays

...
var data8 = new [] { } and int[] data9 = new [] { } are not compilable.
...

And maybe to this MSDN article -which gives less details btw-

edited May 23 '17 at 12:31

Community

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answered Mar 21 '16 at 15:05

uTeisT

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score 0 · Answer 5 · answered Apr 14 '16 at 16:26

if you dont wanna explicitly write the type, you can use linq to filter the last array

var foo = new [] {
    new [] {1, 2, 3},
    new [] {3, 4, 5},
    new [] {0}.Where(e => false).ToArray()
};

this way it would work event if you has to change this code to:

var foo = new[] {
    new [] { new { N = 1 }, new { N = 2 }, new { N = 3} },
    new [] { new { N = 3 }, new { N = 4 }, new { N = 5} },
    new [] { new { N = 0 } }.Where(e => false).ToArray()
};

How to have empty array as part of implict array in C#

5 Answers5