我读取文件的时候遇到了一个问题

class MyFile < File
    def foo
        self.each_line do | line |
            puts line
        end
    end
end

file_path = "text_file"

file = MyFile.open(file_path) do | file |
    file.each_line do | line |
        puts line
    end
    file.close
end

输出结果为：

line 1
line 2
line 3

如果通过调用方法输出：

class MyFile < File
    def foo
        self.each_line do | line |
            puts line
        end
    end
end

file_path = "text_file"

my_file = MyFile.open(file_path) do | file |
    file.foo
    file.close
end

输入结果为：

/Users/veightz/Developer/RubyCode/io_error.rb:4:in `write': not opened for writing (IOError)
    from /Users/veightz/Developer/RubyCode/io_error.rb:4:in `puts'
    from /Users/veightz/Developer/RubyCode/io_error.rb:4:in `block in foo'
    from /Users/veightz/Developer/RubyCode/io_error.rb:3:in `each_line'
    from /Users/veightz/Developer/RubyCode/io_error.rb:3:in `foo'
    from /Users/veightz/Developer/RubyCode/io_error.rb:20:in `block in <main>'
    from /Users/veightz/Developer/RubyCode/io_error.rb:19:in `open'
    from /Users/veightz/Developer/RubyCode/io_error.rb:19:in `<main>'

我又添加了一个新方法 bar

class MyFile < File
    def foo
        self.each_line do | line |
            puts line
        end
    end

    def bar
        self.each_line do | line |
            p line
        end
    end
end

my_file = MyFile.open(file_path) do | file |
    file.bar
    file.close
end

输入结果为：

"line 1\n"
"line 2\n"
"line 3\n"

非常困惑，求解释。