## digitalmars.D - Array expression for multi dimensional arrays

- Madhav <unmarshall gmail.com> Mar 23 2011
- spir <denis.spir gmail.com> Mar 23 2011
- Madhav <unmarshall gmail.com> Mar 23 2011
- Don <nospam nospam.com> Mar 23 2011
- Jonathan M Davis <jmdavisProg gmx.com> Mar 23 2011
- Daniel Green <venix1 gmail.com> Mar 23 2011

Hi, I tried to do the following: auto arr = new int[2][2]; arr[] = 1; // using array expressions // The above gives - Error: cannot implicitly convert expression (1) of type int to const(int[2u][]) This was the first step to try out if array arithmetic that worked with single dimensional arrays worked with multi-dimensional. I guess it does not. The immediate utility of this would be to cleanly do matrix algebra. Any ideas why powerful array expressions were not extended to multi dimensional arrays as well? Regards, Madhav

Mar 23 2011

On 03/23/2011 12:01 PM, Madhav wrote:Hi, I tried to do the following: auto arr = new int[2][2]; arr[] = 1; // using array expressions // The above gives - Error: cannot implicitly convert expression (1) of type int to const(int[2u][]) This was the first step to try out if array arithmetic that worked with single dimensional arrays worked with multi-dimensional. I guess it does not. The immediate utility of this would be to cleanly do matrix algebra. Any ideas why powerful array expressions were not extended to multi dimensional arrays as well? Regards, Madhav

IIUC, you can do it level by level only: unittest { int[3] a3; int[3][2] a32; a3[] = 1; a32[] = a3; assert(a32 == [[1,1,1], [1,1,1]]); } Note: in those assignments, [] is optional, but I consider this as a bug. Even more since int[3] a3 = 1; // works int[3][2] a32 = a3 // works not denis -- _________________ vita es estrany spir.wikidot.com

Mar 23 2011

== Quote from spir (denis.spir gmail.com)'s articleOn 03/23/2011 12:01 PM, Madhav wrote:Hi, I tried to do the following: auto arr = new int[2][2]; arr[] = 1; // using array expressions // The above gives - Error: cannot implicitly convert expression (1) of type int to const(int[2u][]) This was the first step to try out if array arithmetic that worked with single dimensional arrays worked with multi-dimensional. I guess it does not. The immediate utility of this would be to cleanly do matrix algebra. Any ideas why powerful array expressions were not extended to multi dimensional arrays as well? Regards, Madhav

unittest { int[3] a3; int[3][2] a32; a3[] = 1; a32[] = a3; assert(a32 == [[1,1,1], [1,1,1]]); } Note: in those assignments, [] is optional, but I consider this as a bug. Even more since int[3] a3 = 1; // works int[3][2] a32 = a3 // works not denis

Yes i guessed that. My question was more to do with extending array expressions for multi dimensional arrays as well. Don't you think this should be provided by the language? It will ease out a lot of mathematical implementations Regards, Madhav

Mar 23 2011

Madhav wrote:== Quote from spir (denis.spir gmail.com)'s articleOn 03/23/2011 12:01 PM, Madhav wrote:

unittest { int[3] a3; int[3][2] a32; a3[] = 1; a32[] = a3; assert(a32 == [[1,1,1], [1,1,1]]); } Note: in those assignments, [] is optional, but I consider this as a bug. Even more since int[3] a3 = 1; // works int[3][2] a32 = a3 // works not denis

Yes i guessed that. My question was more to do with extending array expressions for multi dimensional arrays as well. Don't you think this should be provided by the language? It will ease out a lot of mathematical implementations

The problem is, that with the multi-dimensional case, you generally want STRIDED operations. These are much more complicated, and are much easier to implement in a library rather than in the core language. Belongs in Phobos, no doubt about it. Currently waiting for the enhancement patch in bug 3474 to be applied.

Mar 23 2011

It wouldn't really help in this case, but I would point out that you probably didn't declare the type of array that you meant to (you might have, but most people wouldn't really want the type of array that you declared but _would_ mistakenly use the syntax that you used). You declare an int[2u][], whereas what you probably wanted was an int[][]. You have a dynamic array of static arrays where each static array has a fixed length of 2. If you want a dynamic array of dynamic arrays, you need to do this: auto arr = new int[][](2, 2); - Jonathan M Davis

Mar 23 2011

On 3/23/2011 7:01 AM, Madhav wrote:

I'm not sure this applies to your topic, but it gave me something to play with that may be related. Static arrays are always laid out contiguously in memory. This appears to allow casting to a single dimensional array. auto a = new int[3][2]; int[] test = cast(int[]) a; printf("%d\n", test.length); // Equals 6.

Mar 23 2011