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--- assignments:a2 [2009/04/02 03:21] – jonathan
+++ assignments:a2 [2009/04/05 02:11] (current) – removed jonathan
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-====== Assignment 2 ======
-Download the file a2-money.zip in ''Assignments'' in the SVN. Instructions are in the PDF file ''W09-a2-money-spec.pdf''.
-Since your code will be executed and checked with a script, you must follow the instructions precisely. Your work is in a directory ''a2-money'' (with ecf file as is, in this folder). You must do a written report which you must include in this directory.
-Before submitting, eclean and do a fresh compile and execute to make sure that you get a green bar. Then eclean the directory ''a2-money'' again (to get rid of the EIFGEN's) and submit it:
-   submit -l 3311 a2 a2-money
-Don't forget to also hand in your written report at the 3311 drop box in the CSE building.
-----
-----
-===== void safety and HASH_TABLE [?G, ?K]=====
-  * We would like to use HASH_TABLE[G, H] to implement the efficient version of MAP when we can rely on hashable keys.
-  * Eiffelstudio 6.3 is in transition to implementing void safety (which means that the compiler will always catch errors of the type ''t.f(x)'' where ''t = Void''). As part of the transition, a type with a question mark in front of it (?T) is detachable (allowed to be Void) whereas a type with an exclamation mark (!T) is an attached type (is never allowed to be void).
-  * The latest version of HASH_TABLE inherits from TABLE [?G, ?K], i.e. the generic parameters are allowed to be attached to Void. So, to use HASH_TABLE in HASHABLE_MAP, we can proceed as follows:
-<code eiffel>
-class
-   HASHABLE_MAP [KEY -> {HASHABLE,COMPARABLE}, VAL]
-inherit
-   MAP[?KEY,?VAL]
-create
-   make
-feature
-   has (k: ?KEY):BOOLEAN  ...
-   item alias "[]" (k: ?KEY): ?VAL assign override ...
-   has_tuple(t: TUPLE[k:?KEY; v:?VAL]): BOOLEAN ...
-   domain: ARRAY[?KEY]
-feature{NONE}
-   map_imp: HASH_TABLE[VAL, KEY]
-end
-</code>
-The question mark will ensure that the keys and values can be Void. you may sometimes have to do the following to obtain a correct tuple type:
-<code eiffel>
-t: TUPLE[KEY,VAL]
-t ?= [map_imp.key_for_iteration, map_imp.item_for_iteration]
-</code>
-"?=" is assignment attempt and is discussed in the text book OOSC2.
-In the next version of EiffelStudio, the default will be that when you declare
-<code eiffel>
-t: T
-</code>
-t is attached. You will have to explicitly say
-<code eiffel>
-t: ?T
-</code>
-if you want to allow ''t = Void''.