[Libguestfs] [PATCH v6 2/3] mllib: modify nsplit to take optional noempty and count arguments

[Tomáš Golembiovský]

On Tue, 31 Jan 2017 11:35:01 +0000
"Richard W.M. Jones" <rjones at redhat.com> wrote:

> On Mon, Jan 30, 2017 at 10:43:15PM +0100, Tomáš Golembiovský wrote:
> > Added two new optional arguments to nsplit:
> > 
> > * keep_empty: if set to false empty elements are not stored in the
> >   returned list. The default is to keep the empty elements  
> 
> The ?keep_empty flag is pointless.  It's simpler and more
> clear to write:
> 
>   List.filter ((<>) "") (nsplit ...)
> 
> when you don't want empty elements.

That's not entirely true when keep_empty is used in combination with
count. When keep_empty is false then the split is not considered a
(successful) split and internal state of count is not decreased.

Example:

# List.filter ((<>) "") (nsplit  ~count:3 "," "a,,,b,,,c,,d" ) ;;
  - : string list = ["a"; "b,,,c,,d"]

# nsplit ~keep_empty:false ~count:3 "," "a,,,b,,,c,,d" ;;
  - : string list = ["a"; "b"; "c"; ",d"]

> 
> However the ?count flag is fine, since that's what Perl's split
> function also does.
> 
> > -    let rec nsplit sep str =
> > +    let rec nsplit ?(keep_empty = true) ?(count = -1) sep str =
> >        let len = length str in
> >        let seplen = length sep in
> >        let i = find str sep in
> > -      if i = -1 then [str]
> > +      if i = -1 || count = 0 then
> > +        if str = "" && not keep_empty then [] else [str]
> >        else (
> >          let s' = sub str 0 i in
> >          let s'' = sub str (i+seplen) (len-i-seplen) in
> > -        s' :: nsplit sep s''
> > +        let elem, count =
> > +          if s' = "" && not keep_empty then
> > +            [], count
> > +          else
> > +            [s'], if count > 0 then count-1 else count
> > +        in
> > +        elem @ nsplit ~keep_empty:keep_empty ~count:count sep s''  
> 
> You can write this line as:
> 
>     elem @ nsplit ~count sep s''
> 
> (after dropping keep_empty).
> 
> Rich.
> 
> -- 
> Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
> Read my programming and virtualization blog: http://rwmj.wordpress.com
> libguestfs lets you edit virtual machines.  Supports shell scripting,
> bindings from many languages.  http://libguestfs.org


-- 
Tomáš Golembiovský <tgolembi at redhat.com>