* Array slices and types @ 2008-08-20 14:51 Maciej Sobczak 2008-08-20 15:26 ` Niklas Holsti ` (4 more replies) 0 siblings, 5 replies; 15+ messages in thread From: Maciej Sobczak @ 2008-08-20 14:51 UTC (permalink / raw) Consider this: type Name is new String (1 .. 10); N : Name; Some_String : String := "abc"; How can I assign Some_String to the beginning slice (ie. to the first three characters) of N? Everything that I can think of (short of copying characters individually) hits the type compatibility problem. -- Maciej Sobczak * www.msobczak.com * www.inspirel.com Database Access Library for Ada: www.inspirel.com/soci-ada ^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: Array slices and types 2008-08-20 14:51 Array slices and types Maciej Sobczak @ 2008-08-20 15:26 ` Niklas Holsti 2008-08-20 15:46 ` Dmitry A. Kazakov ` (3 subsequent siblings) 4 siblings, 0 replies; 15+ messages in thread From: Niklas Holsti @ 2008-08-20 15:26 UTC (permalink / raw) Maciej Sobczak wrote: > Consider this: > > type Name is new String (1 .. 10); > > N : Name; > > Some_String : String := "abc"; > > How can I assign Some_String to the beginning slice (ie. to the first > three characters) of N? > Everything that I can think of (short of copying characters > individually) hits the type compatibility problem. One way is to assign all of N: N := Name (Some_String(1..3) & String (N(4..10))); Another way is to use a helpful procedure: procedure Set (Target : out String; Source : in String) is begin Target := Source; end Set; and use type "conversion" on the output parameter: Set (Target => String (N(1..3)), Source => Some_String(1..3)); That is equivalent to the (forbidden): String (N(1..3)) := Some_String(1..3); -- Not Ada! -- Niklas Holsti Tidorum Ltd niklas holsti tidorum fi . @ . ^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: Array slices and types 2008-08-20 14:51 Array slices and types Maciej Sobczak 2008-08-20 15:26 ` Niklas Holsti @ 2008-08-20 15:46 ` Dmitry A. Kazakov 2008-08-20 18:52 ` Niklas Holsti 2008-08-20 17:47 ` stefan-lucks ` (2 subsequent siblings) 4 siblings, 1 reply; 15+ messages in thread From: Dmitry A. Kazakov @ 2008-08-20 15:46 UTC (permalink / raw) On Wed, 20 Aug 2008 07:51:02 -0700 (PDT), Maciej Sobczak wrote: > Consider this: > > type Name is new String (1 .. 10); > > N : Name; > > Some_String : String := "abc"; > > How can I assign Some_String to the beginning slice (ie. to the first > three characters) of N? > Everything that I can think of (short of copying characters > individually) hits the type compatibility problem. You need an unconstrained base type for this. In your case the base is anonymous. So name it: type Name_Base is new String; -- The base type is now named subtype Name is Name_Base (1..10); N : Name; Some_String : String := "abc"; begin N (1..3) := Name_Base (Some_String); -- Regards, Dmitry A. Kazakov http://www.dmitry-kazakov.de ^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: Array slices and types 2008-08-20 15:46 ` Dmitry A. Kazakov @ 2008-08-20 18:52 ` Niklas Holsti 2008-08-20 20:01 ` Simon Wright 0 siblings, 1 reply; 15+ messages in thread From: Niklas Holsti @ 2008-08-20 18:52 UTC (permalink / raw) Dmitry A. Kazakov wrote: > On Wed, 20 Aug 2008 07:51:02 -0700 (PDT), Maciej Sobczak wrote: > > >>Consider this: >> >> type Name is new String (1 .. 10); >> >> N : Name; >> >> Some_String : String := "abc"; >> >>How can I assign Some_String to the beginning slice (ie. to the first >>three characters) of N? >>Everything that I can think of (short of copying characters >>individually) hits the type compatibility problem. > > > You need an unconstrained base type for this. In your case the base is > anonymous. So name it: > > type Name_Base is new String; -- The base type is now named > subtype Name is Name_Base (1..10); > N : Name; > Some_String : String := "abc"; > begin > N (1..3) := Name_Base (Some_String); Or you can use the 'Base attribute: N(1..3) := Name'Base (Some_String(1..3)); -- Niklas Holsti Tidorum Ltd niklas holsti tidorum fi . @ . ^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: Array slices and types 2008-08-20 18:52 ` Niklas Holsti @ 2008-08-20 20:01 ` Simon Wright 2008-08-21 5:26 ` Niklas Holsti 0 siblings, 1 reply; 15+ messages in thread From: Simon Wright @ 2008-08-20 20:01 UTC (permalink / raw) Niklas Holsti <niklas.holsti@tidorum.invalid> writes: > Or you can use the 'Base attribute: > > N(1..3) := Name'Base (Some_String(1..3)); Only for scalar types, says GNAT. ^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: Array slices and types 2008-08-20 20:01 ` Simon Wright @ 2008-08-21 5:26 ` Niklas Holsti 2008-08-21 8:53 ` Dmitry A. Kazakov 0 siblings, 1 reply; 15+ messages in thread From: Niklas Holsti @ 2008-08-21 5:26 UTC (permalink / raw) Simon Wright wrote: > Niklas Holsti <niklas.holsti@tidorum.invalid> writes: > > >>Or you can use the 'Base attribute: >> >> N(1..3) := Name'Base (Some_String(1..3)); > > > Only for scalar types, says GNAT. Oops... GNAT 3.15p accepted 'Base for the array type. But the LRM indeed allows it only for scalar types, so this is a bug (or "extension" :-) in 3.15p. Sorry for my misinformation (and I know I should use a newer GNAT). But doesn't this example show that it would be useful to have 'Base also for array types? Any strong reasons against it? -- Niklas Holsti Tidorum Ltd niklas holsti tidorum fi . @ . ^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: Array slices and types 2008-08-21 5:26 ` Niklas Holsti @ 2008-08-21 8:53 ` Dmitry A. Kazakov 2008-08-21 14:44 ` Adam Beneschan 0 siblings, 1 reply; 15+ messages in thread From: Dmitry A. Kazakov @ 2008-08-21 8:53 UTC (permalink / raw) On Thu, 21 Aug 2008 08:26:26 +0300, Niklas Holsti wrote: > But doesn't this example show that it would be useful to have 'Base > also for array types? For any type, actually. Consider this language design fault: procedure Initialize (X : in out S) is begin Initialize (T (X)); ... -- My stuff end Initialize; A call to Initialize should be done automatically, but it is not. So the parent of S must be explicitly specified and known to all descendant. This is a really *bad* thing: package Foo is type S is new T with private; private type S is new Private_Decendant_Of_T with ...; end Foo; What would happen if Private_Decendant_Of_T overrode Initialize of T? The result would be an inability to publicly derive from S any new types if Initialize should be extended! S'Base could mend it: procedure Initialize (X : in out S) is begin (S"Base (X)).Initialize; -- Call to parent whatever it be ... -- My stuff end Initialize; Presently the only way is to override Initialize, Finalize and Adjust everywhere, even if you actually don't want to extend them: package Foo is type S is new T with private; overriding procedure Initialize (X : in out S); -- Have to do this! private type S is new Private_Decendant_Of_T with ...; end Foo; -- Regards, Dmitry A. Kazakov http://www.dmitry-kazakov.de ^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: Array slices and types 2008-08-21 8:53 ` Dmitry A. Kazakov @ 2008-08-21 14:44 ` Adam Beneschan 2008-08-21 15:46 ` Dmitry A. Kazakov 2008-08-22 4:30 ` Randy Brukardt 0 siblings, 2 replies; 15+ messages in thread From: Adam Beneschan @ 2008-08-21 14:44 UTC (permalink / raw) On Aug 21, 1:53 am, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de> wrote: > On Thu, 21 Aug 2008 08:26:26 +0300, Niklas Holsti wrote: > > But doesn't this example show that it would be useful to have 'Base > > also for array types? > > For any type, actually. > > Consider this language design fault: > > procedure Initialize (X : in out S) is > begin > Initialize (T (X)); > ... -- My stuff > end Initialize; > > A call to Initialize should be done automatically, but it is not. So the > parent of S must be explicitly specified and known to all descendant. This > is a really *bad* thing: > > package Foo is > type S is new T with private; > private > type S is new Private_Decendant_Of_T with ...; > end Foo; > > What would happen if Private_Decendant_Of_T overrode Initialize of T? The > result would be an inability to publicly derive from S any new types if > Initialize should be extended! > > S'Base could mend it: > > procedure Initialize (X : in out S) is > begin > (S"Base (X)).Initialize; -- Call to parent whatever it be > ... -- My stuff > end Initialize; Sorry, Dmitry, but if you'll pardon the expression, you're a little off-base here. S'Base and S are subtypes of the same *type*. They may be different subtypes (have different constraints), but they're the same type. You're asking for an attribute that would give you a different type. There may be merit in having such an attribute (I haven't looked into it closely), but calling it 'Base would be a bad idea. S'Parent might be better. Niklas is asking for S'Base to be the unconstrained array subtype of the (possibly constrained) array subtype S. It would still fit into the definition of 'Base (3.5(15)). I'm not sure why this wasn't defined for array subtypes, or for any other type that could have discriminants; offhand I don't see how this would cause any problems. -- Adam ^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: Array slices and types 2008-08-21 14:44 ` Adam Beneschan @ 2008-08-21 15:46 ` Dmitry A. Kazakov 2008-08-22 4:30 ` Randy Brukardt 1 sibling, 0 replies; 15+ messages in thread From: Dmitry A. Kazakov @ 2008-08-21 15:46 UTC (permalink / raw) On Thu, 21 Aug 2008 07:44:29 -0700 (PDT), Adam Beneschan wrote: > Sorry, Dmitry, but if you'll pardon the expression, you're a little > off-base here. S'Base and S are subtypes of the same *type*. No need to excuse, you are right, I don't see any semantic difference between subtypes of "same" type and derived tagged types. Consequently, I don't think it is worth to further maintain such difference in the language. > They > may be different subtypes (have different constraints), but they're > the same type. You're asking for an attribute that would give you a > different type. Yep, for that matter, tag is merely a constraint put on T'Class. Ada 83 model is capable to incorporate OO! We always knew that! (:-)) > There may be merit in having such an attribute (I > haven't looked into it closely), but calling it 'Base would be a bad > idea. S'Parent might be better. Integer'Parent were Universal_Integer, I guess (:-)) > Niklas is asking for S'Base to be the unconstrained array subtype of > the (possibly constrained) array subtype S. It would still fit into > the definition of 'Base (3.5(15)). I'm not sure why this wasn't > defined for array subtypes, or for any other type that could have > discriminants; offhand I don't see how this would cause any problems. I think that the reason was that S'Base was thought as a very low-level thing, something like the least constrained type of the *same* internal representation. For unconstrained arrays the representation is likely not the same, they might have a dope. For other types nobody seemingly cared. (:-)) IMO, if S'Base need to be extended, then that would require a bit firmer foundation than the above. -- Regards, Dmitry A. Kazakov http://www.dmitry-kazakov.de ^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: Array slices and types 2008-08-21 14:44 ` Adam Beneschan 2008-08-21 15:46 ` Dmitry A. Kazakov @ 2008-08-22 4:30 ` Randy Brukardt 1 sibling, 0 replies; 15+ messages in thread From: Randy Brukardt @ 2008-08-22 4:30 UTC (permalink / raw) "Adam Beneschan" <adam@irvine.com> wrote in message news:fc112b42-285c-4ed5-ae78-34be4e60f6df@i20g2000prf.googlegroups.com... > On Aug 21, 1:53 am, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de> > wrote: >> On Thu, 21 Aug 2008 08:26:26 +0300, Niklas Holsti wrote: >> > But doesn't this example show that it would be useful to have 'Base >> > also for array types? >> >> For any type, actually. >> >> Consider this language design fault: >> >> procedure Initialize (X : in out S) is >> begin >> Initialize (T (X)); >> ... -- My stuff >> end Initialize; >> >> A call to Initialize should be done automatically, but it is not. So the >> parent of S must be explicitly specified and known to all descendant. >> This >> is a really *bad* thing: >> >> package Foo is >> type S is new T with private; >> private >> type S is new Private_Decendant_Of_T with ...; >> end Foo; >> >> What would happen if Private_Decendant_Of_T overrode Initialize of T? The >> result would be an inability to publicly derive from S any new types if >> Initialize should be extended! >> >> S'Base could mend it: >> >> procedure Initialize (X : in out S) is >> begin >> (S"Base (X)).Initialize; -- Call to parent whatever it be >> ... -- My stuff >> end Initialize; > > Sorry, Dmitry, but if you'll pardon the expression, you're a little > off-base here. S'Base and S are subtypes of the same *type*. They > may be different subtypes (have different constraints), but they're > the same type. You're asking for an attribute that would give you a > different type. There may be merit in having such an attribute (I > haven't looked into it closely), but calling it 'Base would be a bad > idea. S'Parent might be better. I tried to propose such a thing for Ada 2005, but it didn't work out. There isn't necessarily a single type that is the parent, unless you break privacy. Specifically: package P is type New_Type is new Some_Base with private; procedure Some_Operation (Obj : in out New_Type; Parent : in New_Type'Parent); private type New_Type is new Some_Derived with record ... end P; In this case, what does New_Type'Parent give you in the body? We'd want it to resolve to Some_Derived. But a client of P can't see the full declaration (and shouldn't be able to depend on it), and thus P.New_Type'Parent would have to resolve to Some_Base. So far, we can live with this. But now consider the completion to Some_Operation: the body would use the same parameter types in order to conform, but the *meaning* of the second parameter would be different to clients and the body. Oops. One could ban using this attribute in such specs, but that looks like a nasty wart (as bad as the original one). Thus, we didn't get a 'Parent attribute. > Niklas is asking for S'Base to be the unconstrained array subtype of > the (possibly constrained) array subtype S. It would still fit into > the definition of 'Base (3.5(15)). I'm not sure why this wasn't > defined for array subtypes, or for any other type that could have > discriminants; offhand I don't see how this would cause any problems. It does cause problems, and they're pretty severe as I recall. After all, Ada 83 allowed 'Base on everything (but only as a prefix of another attribute). That was removed in Ada 95 because of problems. But I can't remember what they were precisely. Sorry about that. Randy. ^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: Array slices and types 2008-08-20 14:51 Array slices and types Maciej Sobczak 2008-08-20 15:26 ` Niklas Holsti 2008-08-20 15:46 ` Dmitry A. Kazakov @ 2008-08-20 17:47 ` stefan-lucks 2008-08-20 17:51 ` stefan-lucks 2008-08-20 20:45 ` Adam Beneschan 2008-08-23 2:50 ` Steve 4 siblings, 1 reply; 15+ messages in thread From: stefan-lucks @ 2008-08-20 17:47 UTC (permalink / raw) On Wed, 20 Aug 2008, Maciej Sobczak wrote: > Consider this: > > type Name is new String (1 .. 10); > > N : Name; > > Some_String : String := "abc"; > > How can I assign Some_String to the beginning slice (ie. to the first > three characters) of N? Some_String does always contain exactly ten characters, no more, no less. But you can assign the first three characters of Some_String to name: N(1 .. 3) := Some_String; > Everything that I can think of (short of copying characters > individually) hits the type compatibility problem. Here is a completely compilable example: with Ada.Text_IO; procedure Slice is S: String(1 .. 3); T: String(1 .. 5) := (others => '*'); U: String(1 .. 9) := (others => '-'); begin S := T(1 .. 3); U(1 .. 5) := T; Ada.Text_IO.Put_Line(S & "|" & T & "|" & U); end Slice; As expected, the output is a line with the string "***|*****|*****----". -- ------ Stefan Lucks -- Bauhaus-University Weimar -- Germany ------ Stefan dot Lucks at uni minus weimar dot de ------ I love the taste of Cryptanalysis in the morning! ------ ^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: Array slices and types 2008-08-20 17:47 ` stefan-lucks @ 2008-08-20 17:51 ` stefan-lucks 0 siblings, 0 replies; 15+ messages in thread From: stefan-lucks @ 2008-08-20 17:51 UTC (permalink / raw) > > type Name is new String (1 .. 10); > > > > N : Name; > > > > Some_String : String := "abc"; > > > > How can I assign Some_String to the beginning slice (ie. to the first > > three characters) of N? > > Some_String does always contain exactly ten characters, no more, no less. Sorry, Some_String always contains exactly three characters, name contains ten. -- ------ Stefan Lucks -- Bauhaus-University Weimar -- Germany ------ Stefan dot Lucks at uni minus weimar dot de ------ I love the taste of Cryptanalysis in the morning! ------ ^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: Array slices and types 2008-08-20 14:51 Array slices and types Maciej Sobczak ` (2 preceding siblings ...) 2008-08-20 17:47 ` stefan-lucks @ 2008-08-20 20:45 ` Adam Beneschan 2008-08-21 21:16 ` Maciej Sobczak 2008-08-23 2:50 ` Steve 4 siblings, 1 reply; 15+ messages in thread From: Adam Beneschan @ 2008-08-20 20:45 UTC (permalink / raw) On Aug 20, 7:51 am, Maciej Sobczak <see.my.homep...@gmail.com> wrote: > Consider this: > > type Name is new String (1 .. 10); > > N : Name; > > Some_String : String := "abc"; > > How can I assign Some_String to the beginning slice (ie. to the first > three characters) of N? > Everything that I can think of (short of copying characters > individually) hits the type compatibility problem. Do you really need a new *type*, as opposed to: subtype Name is String (1 .. 10); ??? (The answer may be yes. But I would not declare Name to be a new *type*, rather than a subtype, unless there's a reason for this---such as Name being declared earlier as a private type. I just wanted to make sure that you were aware that declaring a subtype is a possibility.) -- Adam ^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: Array slices and types 2008-08-20 20:45 ` Adam Beneschan @ 2008-08-21 21:16 ` Maciej Sobczak 0 siblings, 0 replies; 15+ messages in thread From: Maciej Sobczak @ 2008-08-21 21:16 UTC (permalink / raw) On 20 Sie, 22:45, Adam Beneschan <a...@irvine.com> wrote: > Do you really need a new *type*, as opposed to: > > subtype Name is String (1 .. 10); > > ??? Good question. If I make it a subtype, then I have no protection against mixing First_Name with Device_Name with File_Name with Signal_Name with Any_Other_Name - and that would defeat the whole purpose of defining them. Consider: declare subtype First_Name is String (1 .. 4); subtype Device_Name is String (1 .. 4); Someone : First_Name := "Adam"; Something : Device_Name := "usb1"; begin Someone := Something; -- oops end; That's why I was thinking about distinct types. I'm OK with type casts when assigning them from regular String. -- Maciej Sobczak * www.msobczak.com * www.inspirel.com Database Access Library for Ada: www.inspirel.com/soci-ada ^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: Array slices and types 2008-08-20 14:51 Array slices and types Maciej Sobczak ` (3 preceding siblings ...) 2008-08-20 20:45 ` Adam Beneschan @ 2008-08-23 2:50 ` Steve 4 siblings, 0 replies; 15+ messages in thread From: Steve @ 2008-08-23 2:50 UTC (permalink / raw) "Maciej Sobczak" <see.my.homepage@gmail.com> wrote in message news:5886ab95-8744-4b72-b911-e4cb8889c7e7@d1g2000hsg.googlegroups.com... > Consider this: > > type Name is new String (1 .. 10); > > N : Name; > > Some_String : String := "abc"; > > How can I assign Some_String to the beginning slice (ie. to the first > three characters) of N? > Everything that I can think of (short of copying characters > individually) hits the type compatibility problem. If you can change the definition of Name to: subtype Name is String( 1 .. 10 ); Then of course you can use: N( 1 .. 3 ) := Some_String( 1 .. 3 ); But that doesn't sound like what you're looking for. Regards, Steve > > -- > Maciej Sobczak * www.msobczak.com * www.inspirel.com > > Database Access Library for Ada: www.inspirel.com/soci-ada ^ permalink raw reply [flat|nested] 15+ messages in thread
end of thread, other threads:[~2008-08-23 2:50 UTC | newest] Thread overview: 15+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2008-08-20 14:51 Array slices and types Maciej Sobczak 2008-08-20 15:26 ` Niklas Holsti 2008-08-20 15:46 ` Dmitry A. Kazakov 2008-08-20 18:52 ` Niklas Holsti 2008-08-20 20:01 ` Simon Wright 2008-08-21 5:26 ` Niklas Holsti 2008-08-21 8:53 ` Dmitry A. Kazakov 2008-08-21 14:44 ` Adam Beneschan 2008-08-21 15:46 ` Dmitry A. Kazakov 2008-08-22 4:30 ` Randy Brukardt 2008-08-20 17:47 ` stefan-lucks 2008-08-20 17:51 ` stefan-lucks 2008-08-20 20:45 ` Adam Beneschan 2008-08-21 21:16 ` Maciej Sobczak 2008-08-23 2:50 ` Steve
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox