Pass a print function for UDTs

[rayegun]

It'd be very nice to replace (1,1) [user-defined value] with the actual value using a user provided print function of some sort. I'm not sure what signature the function pointer would have, but I'm sure it shouldn't be difficult.

[DrTimothyAldenDavis]

This would be nice to have too. I see two different approaches for this. One method would be to add a function pointer to the user-defined GrB_Type object. This might be tricky since it would affect all uses of that GrB_Type. Another would be to pass in a function pointer to GxB_*_fprint, for * = Monoid, Scalar, Vector, and Matrix, which would be a more local revision. It wouldn't change the GrB_Type itself. It could even be used to print built-in types.

Maybe I could just add this as 4 new functions, like GxB_Matrix_fprintf with signature:

GrB_Info GxB_Matrix_fprintf ( GrB_Matrix A, const char *name, GxB_Print_Level pr, FILE *f, GxB_format_function *f) ;

or something, which adds the function pointer f that would define how to print a scalar.

See Source/GB_code_check.c and grep for FUTURE. I already have tagged this as a future extension that would be nice to have.

[DrTimothyAldenDavis]

The GxB_format_function should probably have the signature:

typedef void (*GxB_format_function) (char *, const void *)

where the const void is the scalar to print, and the char * would be an array of some large fixed size which is then filled with the string that should be printed. I would want to use the char * instead of FILE * because I already have a way to define a printf function for SuiteSparse:GraphBLAS to use.

[rayegun]

What size do you estimate for the char array?

[DrTimothyAldenDavis]

I could just create some large static-size array, say 2048 or something big, with a #define that gives the size.

[DrTimothyAldenDavis]

A better approach would be to have a user-provided function that can do one of two things: (a) return the size of the string required to print a specific user-defined value, and (b) fill a string (provided by GraphBLAS) with the printed value itself. Then I could use a dynamically allocated array, with no limits on the size of the string.