107 lines
2.5 KiB
Ruby
107 lines
2.5 KiB
Ruby
require File.expand_path(File.dirname(__FILE__) + '/edgecase')
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class AboutSandwichCode < EdgeCase::Koan
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def count_lines(file_name)
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file = open(file_name)
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count = 0
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while line = file.gets
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count += 1
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end
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count
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ensure
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file.close if file
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end
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def test_counting_lines
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assert_equal __, count_lines("example_file.txt")
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end
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# ------------------------------------------------------------------
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def find_line(file_name)
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file = open(file_name)
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while line = file.gets
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return line if line.match(/e/)
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end
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ensure
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file.close if file
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end
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def test_finding_lines
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assert_equal __, find_line("example_file.txt")
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end
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# ------------------------------------------------------------------
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# THINK ABOUT IT:
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#
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# The count_lines and find_line are similar, and yet different.
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# They both follow the pattern of "sandwich code".
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#
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# Sandwich code is code that comes in three parts: (1) the top slice
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# of bread, (2) the meat, and (3) the bottom slice of bread. The
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# the bread part of the sandwich almost always goes together, but
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# the meat part changes all the time.
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#
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# Because the changing part of the sandwich code is in the middle,
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# abstracting the top and bottom bread slices to a library can be
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# difficult in many languages.
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#
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# (Aside for C++ programmers: The idiom of capturing allocated
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# pointers in a smart pointer constructor is an attempt to deal with
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# the problem of sandwich code for resource allocation.)
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#
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# Consider the following code:
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#
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def file_sandwich(file_name)
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file = open(file_name)
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yield(file)
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ensure
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file.close if file
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end
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# Now we write:
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def count_lines2(file_name)
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file_sandwich(file_name) do |file|
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count = 0
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while line = file.gets
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count += 1
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end
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count
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end
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end
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def test_counting_lines2
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assert_equal __, count_lines2("example_file.txt")
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end
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# ------------------------------------------------------------------
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def find_line2(file_name)
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# Rewrite find_line using the file_sandwich library function.
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end
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def test_finding_lines2
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assert_equal __, find_line2("example_file.txt")
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end
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# ------------------------------------------------------------------
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def count_lines3(file_name)
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open(file_name) do |file|
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count = 0
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while line = file.gets
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count += 1
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end
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count
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end
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end
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def test_open_handles_the_file_sandwich_when_given_a_block
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assert_equal __, count_lines3("example_file.txt")
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end
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end
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