Matrix-type-friendly syntax and more

[Denis Shelomovskij]

09.10.2011 21:29, bearophile пишет:
> Kenji Hara has just copied in GIT a large patch by Don:
> https://github.com/9rnsr/dmd/branches/opDollar
>
> It allows user defined collections usable with this syntax:
>
> x[$-2, y[$-6, $-9], $-2]
>
> See:
> http://d.puremagic.com/issues/show_bug.cgi?id=3474
>
>
> But a syntax like this too is quite important for a user-defined matrix type to be used in numerical code:
>
> m[i..j, k..w]
>
> Similar slicing and dicing of arrays is used all the time in NumPy (array library for Python) code.
>
> This is a comment by Don about it:
>
>> (4) I have NOT implemented $ inside opSlice(), opSliceAssign().
>> It could be done, but I believe those language features need work. They don't
>> permit multi-dimensional slicing. I think they should be removed, and the
>> functionality folded into opIndex.
>
> Isn't it better to improve opSlice() instead of deprecating it?
>
>
> I don't remember if people appreciate the idea of a stride (like the third step argument of std.range.iota), this too is used in scientific array-oriented code:
>
> m[i..j:2, k..w:3]
>
> ---------------
>
> In Python code there is often the need for a good multi-dimensional array type, even in not-scientific code.
>
> In the Python standard library there is a array module, but it's almost a joke, it's 1D, and it's not used much:
> http://docs.python.org/library/array.html
>
> Python programmers use the multi-dimensional array of NumPy, it's widely used around the world, it's used by SciPy too (a scientific programming library).
>
> The experience of Python, with its sorely felt lack of a good multi-dimensional array type, the failure of its array module, and the success of NumPy, the problems caused by two precedent incompatible array libraries Numeric (http://people.csail.mit.edu/jrennie/python/numeric/ ) and numarray (http://www.stsci.edu/resources/software_hardware/numarray/numarray.html), tells me that it will be good to have a bare-bones, but efficient multi-dimensional array type. Plus external libraries (not present in Phobos) that use those arrays to implement all the things they want.
>
> I think that's a good tradeoff between the opposed needs of:
> - Keeping Phobos of reasonable size (to not increase too much the burden of its management, to not slow down too much its development);
> - Avoiding the risk of incompatible multi-dimensional array types. Most code out there is able to build on a common foundation. This avoids duplication (like the creation of Python numarray and Numeric), allows a better focusing of efforts and speeds up the development of a language-wide standard for such arrays;
> - Offer a nD array type to the casual D programmer, even one that doesn't want or can't install other libraries. Even some 30-lines long D programs need multi-dimensional arrays, but they often don't need a complex scientific library too (example of a problem: in the preconditions of my functions that take an array of arrays I always have to test the input is not jagged and it is a rectangular matrix. Such test is not necessary for a multi-dimensional array that is never jagged). Putting the bare bones multi-dimensional array type in Phobos allows people to use them with zero other installs.
>
> This multi-dimensional Phobos array type doesn't even need to contain code to invert a matrix or compute determinant, etc. It just needs basic operations like allocation, indexing, multi-dimensional slicing, change of shape, iteration... Everything else is in modules/packages external to Phobos.
>
> I am not suggesting to put a sparse multi-dimensional array type in Phobos. This need is much less common in casual short programs. This is better left to external modules.
>
> Bye,
> bearophile

Suddenly, I had a talk with an Fortran guy at previous weekend and have 
wrote something like Fortran arrays in D last week. I had an idea of 
adding it into Phobos, but just had no time for review of my code. Draft 
version is in attachment.

rarray.d - something like Fortran array
main.d - example of using rarray module
output.txt - main.d output
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