[ruby-core:53930] [ruby-trunk - Feature #8206] Should Ruby core implement String#blank?

Issue #8206 has been updated by headius (Charles Nutter).


marcandre (Marc-Andre Lafortune) wrote:
> Your rb_str_blank is 5-8x faster than regexp? You compared it to `/\A[[:space:]]*\z/ =~ str`?

Regexp matches construct a MatchData and set $~. blank? would do neither, and have no allocation cost whatsoever.
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Feature #8206: Should Ruby core implement String#blank? 
https://bugs.ruby-lang.org/issues/8206#change-38142

Author: sam.saffron (Sam Saffron)
Status: Open
Priority: Normal
Assignee: 
Category: core
Target version: 


There has been some discussion about porting the #blank? protocol over to Ruby in the past that has been rejected by Matz. 

This proposal is only about String however. 

At the moment to figure out if you have a blank string you would 

"  ".strip.length == 0

The disadvantage is that this forces unneeded allocations and does too much work: 

An optimal implementation would be:

static VALUE
rb_str_blank(VALUE str)
{
  rb_encoding *enc;
  char *s, *e;

  enc = STR_ENC_GET(str);
  s = RSTRING_PTR(str);
  if (!s || RSTRING_LEN(str) == 0) return Qtrue;

  e = RSTRING_END(str);
  while (s < e) {
	  int n;
	  unsigned int cc = rb_enc_codepoint_len(s, e, &n, enc);

	  if (!rb_isspace(cc) && cc != 0) return Qfalse;
    s += n;
  }
  return Qtrue;
}

This in turn is about 5-8x than the regex solution to the problem and way faster than allocating one massive string with strip when length is large. 

Should Ruby take on this method, to accompany #strip following its practice. 

--- 

A slight caveat though is that active support has a somewhat different definition of blank? 

const unsigned int as_blank[26] = {9, 0xa, 0xb, 0xc, 0xd,
  0x20, 0x85, 0xa0, 0x1680, 0x180e, 0x2000, 0x2001,
  0x2002, 0x2003, 0x2004, 0x2005, 0x2006, 0x2007, 0x2008,
  0x2009, 0x200a, 0x2028, 0x2029, 0x202f, 0x205f, 0x3000
};

static VALUE
rb_str_blank_as(VALUE str)
{
  rb_encoding *enc;
  char *s, *e;
  int i;
  int found;

  enc = STR_ENC_GET(str);
  s = RSTRING_PTR(str);
  if (!s || RSTRING_LEN(str) == 0) return Qtrue;

  e = RSTRING_END(str);
  while (s < e) {
	  int n;
	  unsigned int cc = rb_enc_codepoint_len(s, e, &n, enc);

    found = 0;
    for(i=0;i<26;i++){
      unsigned int current = as_blank[i];
      if(current == cc) {
        found = 1;
        break;
      }
      if(cc < current){
        break;
      }
    }

	  if (!found) return Qfalse;
    s += n;
  }
  return Qtrue;
}

Clearly it makes no sense to have such a method. 

If Ruby took over implementing String#blank? it would clash with Active Support. But imho would enforce better API consistency. 

Thoughts?


 


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