How to use associative arrays in Ada 2005?
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From: snoopysalive on 21 Nov 2006 05:11 Hi! Can anybody explain me how to use associative arrays in Ada 2005? I mean hashes like in Perl. Some background: I'm a student of Computational Linguistics and try to get away from Perl which I find not efficient enough (at my university, Perl is the standard language used by the professors). In my opinion, C++ is cool but Ada's syntax is better to avoid dirty code. So, when I say "hash", I mean something Perl-like like "$hashname{key1}{key2} = 'something' ". Or something C++-like like "map <string,int> hashname; hashname["key1"] = 42;". Is there anything similar in Ada 2005, too? I bought the book "Programming in Ada 2005" by John Barnes but I don't understand the author's way of explaining a programming language (for me, the book is more confusing than explaining). Or does anybody know a good tutorial similar to the lots of C- and Perl-tutorials? I found many Ada-tutorials but most of them just list the contents of the built-in packages and don't explain how to use them. As a beginner this is confusing. Thanks for every answer! CU, Matthias
From: Georg Bauhaus on 21 Nov 2006 06:49 On Tue, 2006-11-21 at 02:11 -0800, snoopysalive wrote: > So, when I say "hash", I mean something Perl-like like > "$hashname{key1}{key2} = 'something' ". Or something C++-like like "map > <string,int> hashname; hashname["key1"] = 42;". With Ada 2005, you have Ada.Containers.Hashed_Maps; hashname.insert("key1", 42); See http://en.wikibooks.org/wiki/Ada_Programming/Containers#First_Example:_Maps for an example. The original Ada.Containers distribution at http://charles.tigris.org/ has a Containers tutorial linked at the bottom of the page. > I found many Ada-tutorials but most of them just list > the contents of the built-in packages and don't explain how to use > them. As a beginner this is confusing. Maybe try John English's http://burks.bton.ac.uk/burks/language/ada/adacraft/contents.htm It doesn't cover the Ada 2005 containers, though.
From: Matthew Heaney on 21 Nov 2006 09:18 "snoopysalive" <matthias.kistler(a)gmx.de> writes: > Can anybody explain me how to use associative arrays in Ada 2005? I > mean hashes like in Perl. There are actually two kinds of "associative arrays" in Ada05: ordered maps and hashed maps. Each of these container types accept both a key and element as generic formal types. (There are also sets, that accept just an element type.) If both the key and element are "definite" types (types that don't require a constraint to specify the size), then you can use: ada.containers.hashed_maps ada.containers.ordered_maps If either the key or element is an "indefinite" type (such as String), then you can use: ada.containers.indefinite_hashed_maps ada.containers.indefinite_ordered_maps If you use the hashed version, you'll need a hash function for your key type. The library comes with a hash function for type String (and Wide_String, etc); see Ada.Strings.Hash. If you use the ordered version, you'll need a relation operation ("<") for your key type. > In my opinion, C++ is cool but Ada's syntax is > better to avoid dirty code. If you're familiar with the STL, then you should have no trouble with the Ada container library. > So, when I say "hash", I mean something Perl-like like > "$hashname{key1}{key2} = 'something' ". Or something C++-like like "map > <string,int> hashname; hashname["key1"] = 42;". Right. People often say "hash" but in reality that's just one way of implementing an associative container. In Ada05 you can use either the hashed version or the ordered version. Your example above would be: package String_Integer_Maps is new Ada.Containers.Indefinite_Hashed_Maps (String, Integer, Ada.Strings.Hash, Equivalent_Keys => "="); Note that there's no index operator (operator[]()) in Ada, so you say: procedure Op (M : in out String_Integer_Maps.Map) is begin M.Include ("key1", 42); end; Note that this is not exactly equivalent to the C++ operation, since in Ada the key is replaced too (if it already exists). That's unnecessary here so a slightly more efficient technique might be: procedure Op (M : in out String_Integer_Maps.Map) is C : Cursor; B : Boolean; begin M.Insert ("key1", 42, C, B); if not B then M.Replace_Element (C, 42); end if; end Op; > Is there anything similar in Ada 2005, too? I bought the book > "Programming in Ada 2005" by John Barnes but I don't understand the > author's way of explaining a programming language (for me, the book is > more confusing than explaining). That book has a chapter (17?) on the container library. If you have a specific question just post here or send me some email. > Or does anybody know a good tutorial similar to the lots of C- and > Perl-tutorials? I found many Ada-tutorials but most of them just list > the contents of the built-in packages and don't explain how to use > them. As a beginner this is confusing. If just gave a tutorial on the Ada05 container library. I can give you the power-point slides or send you a pdf version. Drop me a line if you're interested. But as a said above, the Ada standard container library is very similar to the C++ STL, so if you already know the latter than the former shouldn't be much of a stretch. -Matt
From: snoopysalive on 21 Nov 2006 18:35 Hello! With the help of both of you, I finally made my first steps with Ada-containers. I really thank both of you very much. @Matt: Yes, I'm really interested in the PowerPoint-slides you were writing about. Would you be so kind and send them to me? I'd prefer the pdf-version but I'd be also happy with the PowerPoint-version. I think, you see my e-mail-address in the header of this message. Thank you! Greetz, Matthias
From: snoopysalive on 23 Nov 2006 14:27 Hi! First: @Matt: Thank you for the pdf. It's really useful, but I couldn't write you back because of the email filter. And now, my next question: How to handle "hashes of hashes" in Ada? Here's the code which should contain a package representing a hash of a hash: -- Here, the code begins with Ada.Text_IO, Ada.Strings.Hash, Ada.Containers.Indefinite_Hashed_Maps; use Ada.Text_IO, Ada.Strings, Ada.Containers; procedure book is package Str_Int_Maps is new Ada.Containers.Indefinite_Hashed_Maps (String, Integer, Ada.Strings.Hash, "="); use Str_Int_Maps; package Str_Map_Maps is new Ada.Containers.Indefinite_Hashed_Maps (String, Str_Int_Maps.Map, Ada.Strings.Hash, "="); Ages : Str_Map_Maps.Map; -- That's the "hash of a hash" begin Ages.Insert("family name",Insert("name",23)); end book; -- Here, the code ends The statement "Ages.Insert("family name",Insert("name",23));" doesn't work. So, how is it possible to do something like this in C++: "... map<string, map<string,int>> ages; ages["family name"]["name"] = 23; ...." Thank you and greetings, Matthias
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