gistfile1.txt

ruby-1.9.2-p290 :005 > a = 'foo'; time(10000000) { "jola #{a} misio" }
      user     system      total        real
  8.260000   0.010000   8.270000 (  8.273313)
 => "jola foo misio" 

ruby-1.9.2-p290 :006 > a = 'foo'; time(10000000) { "jola : misio".gsub(':', a) }
      user     system      total        real
 48.940000   0.070000  49.010000 ( 49.054449)
 => "jola foo misio" 

ruby-1.9.2-p290 :007 > l = lambda { |a| "jola #{a} misio" }
 => #<Proc:0x000000028f6f68@(irb):7 (lambda)> 
ruby-1.9.2-p290 :008 > a = 'foo'; time(10000000) { l[a] }
      user     system      total        real
  9.680000   0.020000   9.700000 (  9.703990)
 => "jola foo misio" 
ruby-1.9.2-p290 :009 >