hello=2C
=3B
I'm =3Bworking on ruby koans.

Now I hav= e to do some sandwhich code.
=3B
The exercise looks like this :<= BR> =3B
require File.expand_path(File.dirname(__FILE__) + '/edgecase= ')
class AboutSandwichCode <=3B EdgeCase::Koan
=3B def count_l= ines(file_name)
=3B =3B =3B file =3D open(file_name)
&nb= sp=3B =3B =3B count =3D 0
=3B =3B =3B while line = =3D file.gets
=3B =3B =3B =3B =3B count +=3D 1
&= nbsp=3B =3B =3B end
=3B =3B =3B count
=3B e= nsure
=3B =3B =3B file.close if file
=3B end
&nb= sp=3B def test_counting_lines
=3B =3B =3B assert_equal 4=2C= count_lines("example_file.txt")
=3B end
=3B # ------------= ------------------------------------------------------
=3B def find= _line(file_name)
=3B =3B =3B file =3D open(file_name)
&n= bsp=3B =3B =3B while line =3D file.gets
=3B =3B =3B= =3B =3B return line if line.match(/e/)
=3B =3B =3B= end
=3B ensure
=3B =3B =3B file.close if file
&= nbsp=3B end
=3B def test_finding_lines
=3B =3B =3B = assert_equal "test\n"=2C find_line("example_file.txt")
=3B end
&= nbsp=3B # -----------------------------------------------------------------= -
=3B # THINK ABOUT IT:
=3B #
=3B # The count_lines= and find_line are similar=2C and yet different.
=3B # They both fo= llow the pattern of "sandwich code".
=3B #
=3B # Sandwich c= ode is code that comes in three parts: (1) the top slice
=3B # of b= read=2C (2) the meat=2C and (3) the bottom slice of bread. =3B The
&= nbsp=3B # bread part of the sandwich almost always goes together=2C but
= =3B # the meat part changes all the time.
=3B #
=3B # = Because the changing part of the sandwich code is in the middle=2C
= =3B # abstracting the top and bottom bread slices to a library can be
&n= bsp=3B # difficult in many languages.
=3B #
=3B # (Aside fo= r C++ programmers: The idiom of capturing allocated
=3B # pointers = in a smart pointer constructor is an attempt to deal with
=3B # the= problem of sandwich code for resource allocation.)
=3B #
= =3B # Consider the following code:
=3B #
=3B def file_sandw= ich(file_name)
=3B =3B =3B file =3D open(file_name)
&nbs= p=3B =3B =3B yield(file)
=3B ensure
=3B =3B&nbs= p=3B file.close if file
=3B end
=3B # Now we write:
&nbs= p=3B def count_lines2(file_name)
=3B =3B =3B file_sandwich(= file_name) do |file|
=3B =3B =3B =3B =3B count =3D = 0
=3B =3B =3B =3B =3B while line =3D file.gets
&= nbsp=3B =3B =3B =3B =3B =3B =3B count +=3D 1
&nb= sp=3B =3B =3B =3B =3B end
=3B =3B =3B = =3B =3B count
=3B =3B =3B end
=3B end
= =3B def test_counting_lines2
=3B =3B =3B assert_equal 4=2C = count_lines2("example_file.txt")
=3B end
=3B # ------------= ------------------------------------------------------
=3B def find= _line2(file_name)
=3B =3B =3B # Rewrite find_line using the= file_sandwich library function.
=3B end
=3B def test_findi= ng_lines2
=3B =3B =3B assert_equal __=2C find_line2("exampl= e_file.txt")
=3B end
=3B # --------------------------------= ----------------------------------
=3B def count_lines3(file_name)<= br> =3B =3B =3B open(file_name) do |file|
=3B =3B&n= bsp=3B =3B =3B count =3D 0
=3B =3B =3B =3B = =3B while line =3D file.gets
=3B =3B =3B =3B =3B&nb= sp=3B =3B count +=3D 1
=3B =3B =3B =3B =3B end<= br> =3B =3B =3B =3B =3B count
=3B =3B = =3B end
=3B end
=3B def test_open_handles_the_file_sandwich= _when_given_a_block
=3B =3B =3B assert_equal __=2C count_li= nes3("example_file.txt")
=3B end
end

But I don't get the = principle.
Can anyone explain this to me ?
=3B
Roelof

= =3B