ENH: Convert PyArray_Functions to generalized ufuncs

numpy/numpy/core/include/numpy/ndarraytypes.h

Lines 444 to 554 in 2948673

    
           typedef struct { 
        
                   /* 
        
                    * Functions to cast to most other standard types 
        
                    * Can have some NULL entries. The types 
        
                    * DATETIME, TIMEDELTA, and HALF go into the castdict 
        
                    * even though they are built-in. 
        
                    */ 
        
                   PyArray_VectorUnaryFunc *cast[NPY_NTYPES_ABI_COMPATIBLE]; 
        
                   /* The next four functions *cannot* be NULL */ 
        
                   /* 
        
                    * Functions to get and set items with standard Python types 
        
                    * -- not array scalars 
        
                    */ 
        
                   PyArray_GetItemFunc *getitem; 
        
                   PyArray_SetItemFunc *setitem; 
        
                   /* 
        
                    * Copy and/or swap data.  Memory areas may not overlap 
        
                    * Use memmove first if they might 
        
                    */ 
        
                   PyArray_CopySwapNFunc *copyswapn; 
        
                   PyArray_CopySwapFunc *copyswap; 
        
                   /* 
        
                    * Function to compare items 
        
                    * Can be NULL 
        
                    */ 
        
                   PyArray_CompareFunc *compare; 
        
                   /* 
        
                    * Function to select largest 
        
                    * Can be NULL 
        
                    */ 
        
                   PyArray_ArgFunc *argmax; 
        
                   /* 
        
                    * Function to compute dot product 
        
                    * Can be NULL 
        
                    */ 
        
                   PyArray_DotFunc *dotfunc; 
        
                   /* 
        
                    * Function to scan an ASCII file and 
        
                    * place a single value plus possible separator 
        
                    * Can be NULL 
        
                    */ 
        
                   PyArray_ScanFunc *scanfunc; 
        
                   /* 
        
                    * Function to read a single value from a string 
        
                    * and adjust the pointer; Can be NULL 
        
                    */ 
        
                   PyArray_FromStrFunc *fromstr; 
        
                   /* 
        
                    * Function to determine if data is zero or not 
        
                    * If NULL a default version is 
        
                    * used at Registration time. 
        
                    */ 
        
                   PyArray_NonzeroFunc *nonzero; 
        
                   /* 
        
                    * Used for arange. Should return 0 on success 
        
                    * and -1 on failure. 
        
                    * Can be NULL. 
        
                    */ 
        
                   PyArray_FillFunc *fill; 
        
                   /* 
        
                    * Function to fill arrays with scalar values 
        
                    * Can be NULL 
        
                    */ 
        
                   PyArray_FillWithScalarFunc *fillwithscalar; 
        
                   /* 
        
                    * Sorting functions 
        
                    * Can be NULL 
        
                    */ 
        
                   PyArray_SortFunc *sort[NPY_NSORTS]; 
        
                   PyArray_ArgSortFunc *argsort[NPY_NSORTS]; 
        
                   /* 
        
                    * Dictionary of additional casting functions 
        
                    * PyArray_VectorUnaryFuncs 
        
                    * which can be populated to support casting 
        
                    * to other registered types. Can be NULL 
        
                    */ 
        
                   PyObject *castdict; 
        
                   /* 
        
                    * Functions useful for generalizing 
        
                    * the casting rules. 
        
                    * Can be NULL; 
        
                    */ 
        
                   PyArray_ScalarKindFunc *scalarkind; 
        
                   int **cancastscalarkindto; 
        
                   int *cancastto; 
        
                   PyArray_FastClipFunc *fastclip; 
        
                   PyArray_FastPutmaskFunc *fastputmask; 
        
                   PyArray_FastTakeFunc *fasttake; 
        
                   /* 
        
                    * Function to select smallest 
        
                    * Can be NULL 
        
                    */ 
        
                   PyArray_ArgFunc *argmin; 
        
           } PyArray_ArrFuncs;

I believe that most of the functions in this list should be replaced by generalized ufuncs and this list of function pointers shrunk.

In theory, the PyArray_Descr structure could then become a meta-type in Python parlance ("inheriting" from PyHeapTypeObject ala https://stackoverflow.com/questions/1237266/how-can-inheritance-be-modelled-using-c) and adding remaining fields needed by NumPy. All dtypes would then be "real" Python types --- but we don't need these extra functions.

In particular, the following functions should be (generalized) ufuncs --- others can likely be as well with a bit more thought.

cast -> becomes several cast_to_ functions
argmax, argmin (Create a gufunc form of argmin and argmax #12516)
dotfunc
sort, argsort (Create a gufunc form of sort and argsort #12517)
- sortfunc --> several sortfuncs for each type of sort
- argsortfunc --> several argsortfuncs for each type
fastclipfunc (ENH/DEP: Use a ufunc under the hood for ndarray.clip #12519)
nonzero

This kind of refactor would break the ABI and I would suggest including only in a major release. It would be facilitated by an improved ufunc dispatching system for NumPy as well.

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	typedef struct {
	/*
	* Functions to cast to most other standard types
	* Can have some NULL entries. The types
	* DATETIME, TIMEDELTA, and HALF go into the castdict
	* even though they are built-in.
	*/
	PyArray_VectorUnaryFunc *cast[NPY_NTYPES_ABI_COMPATIBLE];

	/* The next four functions cannot be NULL */

	/*
	* Functions to get and set items with standard Python types
	* -- not array scalars
	*/
	PyArray_GetItemFunc *getitem;
	PyArray_SetItemFunc *setitem;

	/*
	* Copy and/or swap data. Memory areas may not overlap
	* Use memmove first if they might
	*/
	PyArray_CopySwapNFunc *copyswapn;
	PyArray_CopySwapFunc *copyswap;

	/*
	* Function to compare items
	* Can be NULL
	*/
	PyArray_CompareFunc *compare;

	/*
	* Function to select largest
	* Can be NULL
	*/
	PyArray_ArgFunc *argmax;

	/*
	* Function to compute dot product
	* Can be NULL
	*/
	PyArray_DotFunc *dotfunc;

	/*
	* Function to scan an ASCII file and
	* place a single value plus possible separator
	* Can be NULL
	*/
	PyArray_ScanFunc *scanfunc;

	/*
	* Function to read a single value from a string
	* and adjust the pointer; Can be NULL
	*/
	PyArray_FromStrFunc *fromstr;

	/*
	* Function to determine if data is zero or not
	* If NULL a default version is
	* used at Registration time.
	*/
	PyArray_NonzeroFunc *nonzero;

	/*
	* Used for arange. Should return 0 on success
	* and -1 on failure.
	* Can be NULL.
	*/
	PyArray_FillFunc *fill;

	/*
	* Function to fill arrays with scalar values
	* Can be NULL
	*/
	PyArray_FillWithScalarFunc *fillwithscalar;

	/*
	* Sorting functions
	* Can be NULL
	*/
	PyArray_SortFunc *sort[NPY_NSORTS];
	PyArray_ArgSortFunc *argsort[NPY_NSORTS];

	/*
	* Dictionary of additional casting functions
	* PyArray_VectorUnaryFuncs
	* which can be populated to support casting
	* to other registered types. Can be NULL
	*/
	PyObject *castdict;

	/*
	* Functions useful for generalizing
	* the casting rules.
	* Can be NULL;
	*/
	PyArray_ScalarKindFunc *scalarkind;
	int **cancastscalarkindto;
	int *cancastto;

	PyArray_FastClipFunc *fastclip;
	PyArray_FastPutmaskFunc *fastputmask;
	PyArray_FastTakeFunc *fasttake;

	/*
	* Function to select smallest
	* Can be NULL
	*/
	PyArray_ArgFunc *argmin;

	} PyArray_ArrFuncs;

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ENH: Convert PyArray_Functions to generalized ufuncs #12514

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