Re: [bug-gawk] gawk 5.0.1 patch to allow *valid* awk variable names to be assigned to SYMTAB

[pjfarley3]

Apologies for forgetting to CC the list for the last two iterations of this
discussion.  I am correcting that mistake with this reply.

Arnold,

I understand your lack of enthusiasm, particularly after seeing the
unexpected and undesired results when I tried to actually use my proposed
update.

After having reviewed the manual documentation of the gawk extension API, I
tend to agree that what I want to do is most easily done in a new extension
function.

There do appear to be several of the delivered extension function sources I
could use as a model for a relatively simple extension function that
satisfies my use case.

Thank you for your understanding, guidance, and genuine consideration of my
needs.

If I get such an extension operating correctly and robustly, is there any
interest in my contributing that extension to the project?

Regards,

Peter

> -----Original Message-----
> From: address@hidden <address@hidden>
> Sent: Sunday, October 20, 2019 3:08 PM
> To: address@hidden; address@hidden
> Subject: Re: [bug-gawk] gawk 5.0.1 patch to allow *valid* awk variable
names
> to be assigned to SYMTAB
> 
> OK, I understand the use case.  You want to allow for column names that
are not
> used as variables in the program.
> 
> I am not overly enthusiastic about making this change. I think it
encourages
> confusion as to how SYMTAB works and should be used, and leads (or can
easily
> lead) to sloppy programming.
> 
> W.R.T. functions that can create and set variables, these can easily be
written in
> C as a loadable extension; the manual provides the details.  That is
probably the
> easier path to follow than patching gawk itself.
> 
> Thanks,
> 
> Arnold
> 
> <address@hidden> wrote:
> 
> > The actual use case here is for CSV files with column header lines.
> > At BEGINFILE or FNR == 1 time I would like to assign the column header
> > values (checked for valid variable name format first) as real gawk
> > variable names and assign the column number as their value.
> >
> > Assuming a sample CSV like this:
> >
> > Name,Desc,Amount
> > Harry,Item # 1,-30
> > Jeffery,"Groups, Pairs, and stuff",46
> >
> > I would like to be able to write gawk code like the following
> > (assuming FPAT has been set to deconstruct CSV records and without a
> > check for variable name validity to keep it simpler):
> >
> > FNR == 1 { for (i = 1; i <= NF; i++) SYMTAB[$i] = i } $Name ~ /^H/ {
> > process H.* records } $Amount < 0 { process negative amount records }
> >
> > Obviously with Tom's suggestion this can be coded today as:
> >
> > FNR == 1 { for (i = 1; i <= NF; i++) mem[$i] = i }
> > $(mem["Name"]) ~ /^H/ { process H.* records }
> > $(mem("Amount"]) < 0 { process negative amount records }
> >
> > But that alternative is more typing and IMHO much less clear and is
> > also much easier to make typing mistakes while coding.
> >
> > If this is insufficient reason to open up assignment to SYMTAB I will
> > accept your decision, but that is what I was trying to accomplish with
> > the patch I submitted.
> >
> > Alternatively, could (a) builtin function(s) be supplied to DTRT to
> > create dynamic variables and assign values to them? E.G.,
> > create_var($i[,value]) and/or assign_var($i,value).
> >
> > Peter
> >
> > > -----Original Message-----
> > > From: address@hidden <address@hidden>
> > > Sent: Wednesday, October 16, 2019 11:14 AM
> > > To: address@hidden; address@hidden;
> > > address@hidden
> > > Cc: address@hidden
> > > Subject: Re: [bug-gawk] gawk 5.0.1 patch to allow *valid* awk
> > > variable
> > names
> > > to be assigned to SYMTAB
> > >
> > > Peter,
> > >
> > > I have to agree with Tom here. From the snippet you sent, it doesn't
> > > look
> > like
> > > there's a significant advantage to your using SYMTAB.
> > >
> > > Arnold
> > >
> > > Tom Gray <address@hidden> wrote:
> > >
> > > > HI Peter,
> > > >
> > > > Have you considered using your own array instead of SYMTAB[] Lets
> > > > call it mem[] ... to represent some generic storage space.
> > > > Then the index will not have any "nice variable name" restrictions.
> > > >
> > > >         FNR == 1 { for (I = 1; I <= NF; i++) { mem[$i] =
computed_value }
> > > > }
> > > >
> > > >         If ((mem[MyVar] > x) && (mem[MyVar] < y)) { do-something
> > > >
> > > > In my opinion Gawks jagged arrays of arrays are the best thing
> > > > since
> > sliced
> > > bread.
> > > > Combined with recursion and indirect function calls you get
> > > > incredible
> > power.
> > > >
> > > > Do not underestimate the power of portability.  If you write
> > > > something
> > cool,
> > > you want others to be able to use it.
> > > >
> > > > Tom
<Remainder of original chain snipped for brevity>
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