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https://github.com/EiffelSoftware/eiffel-org.git
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created 20.11
git-svn-id: https://svn.eiffel.com/eiffel-org/trunk@2267 abb3cda0-5349-4a8f-a601-0c33ac3a8c38
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eifops
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[[Property:modification_date|Mon, 10 Sep 2018 09:09:25 GMT]]
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[[Property:publication_date|Mon, 10 Sep 2018 09:09:25 GMT]]
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[[Property:uuid|B74D374E-895C-4F22-B95F-656BD78ECD03]]
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[[Property:weight|1000]]
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[[Property:title|Getting a STRING from a NUMERIC object]]
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[[Property:link_title|NUMERIC to STRING]]
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Every class has the `out` method that can be used to get a text version of the object. For a lot of classes, this method returns internal information that is not really useful for the end user. But for every `NUMERIC` class, the `out` method returns a text representation of the number that the `NUMERIC` object represents.
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<code>
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print_integer (a_integer: INTEGER)
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-- Print the value of `a_integer`.
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do
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print (a_integer.out + "%N")
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end
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</code>
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Note that for more advanced conversion, you can also use a conversion class like `FORMAT_DOUBLE`.
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[[Property:modification_date|Mon, 10 Sep 2018 09:06:41 GMT]]
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[[Property:publication_date|Fri, 07 Sep 2018 12:13:00 GMT]]
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[[Property:uuid|78393BBA-9B1E-4523-9881-3D83CEB6A952]]
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[[Property:weight|3000]]
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[[Property:title|Removing object while iterating on a LIST]]
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If you already have the object that you want to remove from the `LIST` you can easily use `prune` and `prune_all`. But if you want to remove objects while iterating on that `LIST`, depending on criteria on the objects contained in the `LIST`, here is what you can do.
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First of all, if you think about removing an object while iterating, I do not recommend using an `across` loop. If you iterate on the list using a `from until loop end`, just remember to use the `LIST.forth` only when you do not use `LIST.remove`.
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For example, let's say we have class `MY_CLASS` with an attribute `has_stopped` and that I want to remove every object of a `LIST` that has this attribute set to `True`. Here is what the code will look like.
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<code>
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removing_stopped (a_list: LIST [MY_CLASS])
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-- Removing every closed element of `a_list`
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do
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from
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a_list.start
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until
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a_list.exhausted
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loop
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if a_list.item.has_stopped then
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a_list.remove
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else
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a_list.forth
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end
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end
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end
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</code>
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[[Property:modification_date|Wed, 17 Apr 2019 14:09:18 GMT]]
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[[Property:publication_date|Thu, 06 Sep 2018 15:17:57 GMT]]
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[[Property:uuid|96077603-DD2D-4D8C-A486-AF4BD066613A]]
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[[Property:weight|2000]]
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[[Property:title|Iterating on a LIST]]
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There are three Eiffel mechanisms to iterate on every element of a `LIST`.
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=== the `across` loop ===
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The `across` can be used on every `ITERABLE` object (including `LIST` objects).
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<code>
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print_elements (a_list: LIST[INTEGER])
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-- Print every elements on `a_list`
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do
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across a_list as ic loop
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print (ic.item.out + "%N")
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end
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end
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</code>
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Note that the temporary variable (`ic` in the example) represents an iterator of the `ITERABLE` object, and not directly an element like in many other languages (like the `for` structure in Python for example).
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=== the `from until` loop syntax===
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This syntax offer more possibilities than the `across` loop, but is riskier.
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<code>
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print_elements (a_list:LIST[INTEGER])
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-- Print every elements on `a_list`
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do
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from
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a_list.start
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until
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a_list.exhausted
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loop
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print (a_list.item.out + "%N")
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a_list.forth
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end
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end
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</code>
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=== Using Eiffel agents and `{LIST}.do_all, ....` ===
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It is possible to use agents in conjunction with the `LIST` features `do_all`, `do_if`, `there_exists`, and `for_all` which are inherited from the class `LINEAR`.
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<code>
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list_traversal_agents
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-- Example of traversing a list with do_all
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local
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a_list: LINKED_LIST [STRING]
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do
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-- Insert some elements in a_list
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create a_list.make
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a_list.extend ("The Moon Is Full")
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a_list.extend ("Master charge")
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a_list.extend ("Black cat bone")
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a_list.do_all (agent {STRING}.append (" - Albert Collins"))
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a_list.do_all (agent print_element)
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end
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print_element (a_element: STRING)
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-- Print `a_element` to standard output
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do
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io.put_string (a_element)
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io.put_new_line
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end
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</code>
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[[Property:modification_date|Wed, 17 Apr 2019 14:06:41 GMT]]
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[[Property:publication_date|Wed, 17 Apr 2019 14:02:25 GMT]]
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[[Property:uuid|5CA34C5D-30F1-4D6F-9FE4-B555E541EA8C]]
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[[Property:weight|4000]]
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[[Property:title|Managing CTRL+C in console application]]
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Normally, if the user uses the CTRL+C keys, the Eiffel application detect it as an error and throw an exception of type <code>OPERATING_SYSTEM_SIGNAL_FAILURE</code>.
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To manage the CTRL+C keys, you can use a <code>rescue</code> clause to detect the exception and a <code>retry</code> mechanism to cancel the exception handling done by the Eiffel runtime.
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To detect the exception, you can <code>inherit</code> from the <code>EXCEPTIONS</code> class and use an attachment test on <code>Exception_manager.last_exception</code>.
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Note that this code does not work on Windows. If used on Windows, the application will quit, but the <code>rescue</code> call is not launched.
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<code>
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note
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description: "Show how to quit an application using CTRL+C (without trace)."
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author: "Louis Marchand"
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date: "Wed, 25 Apr 2018 23:12:33 +0000"
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revision: "0.1"
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class
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APPLICATION
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inherit
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EXCEPTIONS
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create
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make
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feature {NONE} -- Initialization
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make
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-- Launch `Current'.
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local
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l_ctrl_c:BOOLEAN
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do
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if not l_ctrl_c then
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from until False loop
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io.standard_default.put_string ("Press CTRL+C%N")
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io.input.read_line
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end
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else
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io.standard_default.put_string ("%NClosing...%N")
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end
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rescue
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if attached {OPERATING_SYSTEM_SIGNAL_FAILURE}
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Exception_manager.last_exception then
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l_ctrl_c := True
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retry
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end
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end
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end
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</code>
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10
documentation/20.11/eiffel/Tutorials/Mini-HowTo/index.wiki
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10
documentation/20.11/eiffel/Tutorials/Mini-HowTo/index.wiki
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@@ -0,0 +1,10 @@
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[[Property:modification_date|Mon, 10 Sep 2018 09:04:15 GMT]]
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[[Property:publication_date|Mon, 10 Sep 2018 09:04:15 GMT]]
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[[Property:link_title|Mini How-tos]]
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[[Property:uuid|B2E4622A-2495-47DD-9C02-B9940A026EC1]]
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[[Property:weight|0]]
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[[Property:title|Mini How-tos]]
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In this section, you will find little how-tos that you can use to learn some very specific mechanics in Eiffel. Those how-tos are small by design and can be used to show very fundamental, or more advanced, mechanisms for beginners.
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