From: Jacob Fugal <lukfugl@...>
Date: 2006-06-06T00:58:41+09:00
Subject: Re: This is brain dead, but is it stupid?

On 6/4/06, Patrick Hurley <phurley@gmail.com> wrote:
> > So my multiline gsub tempstring "<img src=\"blublock.jpg\"
> > width=\"replace_with_width\" height=\"replace_with_height\">\n"
> > nastiness would become:
> >
> > @barString = %Q(<img src="blublock.jpg" width="%d" height="%d">\n)
> > @htmlString << @barString % [barWidth,barHeight]
>
> Or you could just:
>
> @htmlString = %Q(<img src="blublock.jpg" width="#{barWidth}"
> height="#{barHeight}">\n)

That doesn't benefit from the template string only needing to be built
once. Compare these:

  template = 'T minus %d...'
  15.downto(1) do |i|
    puts(template % i)
  end

vs.

  15.downto(1) do |i|
    puts "T minus #{i}"
  end

I'll admit, I use the latter as well when I'm not concerned with the
performance in that loop. It does look nicer and more compact. But I'm
guessing[0] that the former will be significantly faster when 1) the
number of iterations in the loop is high and 2) the template is
moderately complex. Why? I assume that String#% is implemented in C
using sprintf (or some cousin). So the performance of template % i is
almost entirely related to one very well used and thus well optimized
libc library call. "T minus #{i}" on the other hand involves parsing
of the string to determine interpolation etc. This is probably also
written in C, but involves more work than the quick sprintf call.

Jacob Fugal

[0] Yes, I'm guessing. I haven't actually benchmarked this or looked
at the ruby sources, so I may be wrong.