the returned integer from extract() method of pair_styles

I have a question regarding the returned integer in the extract method of pairs , specifically the variable “dim” in
void *PairLJCharmmCoulLong::extract(const char *str, int &dim).

For this pair the returned value of dim is 2 for the lj parameters and 0 for the cut offs (as shown below).
—pasted from pair_lj_charmm_coul_long.cpp of lammps’ source code:
void *PairLJCharmmCoulLong::extract(const char *str, int &dim)
dim = 2;
if (strcmp(str,“lj14_1”) == 0) return (void *) lj14_1;
if (strcmp(str,“lj14_2”) == 0) return (void *) lj14_2;
if (strcmp(str,“lj14_3”) == 0) return (void *) lj14_3;
if (strcmp(str,“lj14_4”) == 0) return (void *) lj14_4;

dim = 0;
if (strcmp(str,“implicit”) == 0) return (void *) &implicit;
if (strcmp(str,“cut_coul”) == 0) return (void *) &cut_coul;

return NULL;

I examined some functions (such as ppm.cpp) that called the extract( some_char*,dim ) method.
—pasted from pppm.cpp of lammps’ source code:
int itmp = 0;
double *p_cutoff = (double *) force->pair->extract(“cut_coul”,itmp);
if (p_cutoff == NULL)
error->all(FLERR,“KSpace style is incompatible with Pair style”);
cutoff = *p_cutoff;

In above pasted code the variable &dim from the extract of the pair is stored in itmp however it seems to me that the pppm does not use the itmp any further.

I haven’ yet figured out the &dim variable returned from the extract() of the pairs, and my question is:
For a ‘new/custom’ defined/codded pair-wise additive pair_style (call it:“PairACustomBuiltPairCutCoulLong”) should the returned int at &dim from the extract method of this pairstyle:
void *PairACustomBuiltPairCutCoulLong::extract(const char *str, int &dim){…}

be dim=2 for the van der Waals parameters and dim=0 for cut offs? Or what other values should have?

Thank you.

dim indicates the dimensionality of the pointer returned by Pair::extract().
since the function returns a void pointer, one needs to know what kind of pointer to cast to.

dim == 0 => pointer to a single double precision floating point number
dim == 1 => pointer to a 1d double array
dim == 2 => pointer to a 2d double array