for S'Image use Func??
in [ADA]
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From: Warren on 6 May 2010 15:50 Jeffrey R. Carter expounded in news:hrv32p$nnu$1(a)tornado.tornevall.net: > Warren wrote: >> >> type LNumber_Type is range 0..99_999; >> >> Can I declare.. >> >> for LNumber_Type'Image use LNumber_To_String; > > No. Nor can I see why you'd want to. Once you declare > > function Image (Value : Lnumber_Type) return String; > > why would you want to write > > Lnumber_Type'Image (I) > > rather than > > Image (I) > > ? I agree that it is indeed clumsier. It's just that I tend to use it a lot in debug output, rather than chasing down the package prefix for the To_String() function. I know I can always get away with: Put_Line("The value V=" & T'Image(V)); But everyone has convinced me that it is not a good practice, even if it were allowed. :) Warren
From: Warren on 6 May 2010 15:52 Adam Beneschan expounded in news:2318cabb-080c-42a0-8219-21c347abe172 @o11g2000yqj.googlegroups.com: >> �type LNumber_Type is range 0..99_999; >> >> Can I declare.. >> >> �for LNumber_Type'Image use LNumber_To_String; > > No. > > Broadly, you can't use a FOR attribute specification on every > attribute, just a few select ones that the language specifically says > you can. 'Image isn't one of those. > > I think it's been mentioned a few times on this newsgroup that it > might be nice to have this ability, but I don't see that anyone has > submitted an actual language change proposal. > > -- Adam There's probably bigger fish to fry, I suppose. I'm just being a typical lazy programmer (not always wanting to lookup the correct package prefix for the To_String() function to use). Warren
From: Warren on 6 May 2010 16:04 =?utf-8?Q?Yannick_Duch=C3=AAne_=28Hibou57?= =?utf-8?Q?=29?= expounded in news:op.vcaqajn0ule2fv(a)garhos: > Le Thu, 06 May 2010 19:10:20 +0200, Warren <ve3wwg(a)gmail.com> a > écrit: > >> I have tried to google for this and have not yet found >> a suitable answer, so I'll troll, er, poll for an >> answer here.. >> >> Is there the ability to substitute your own S'Image >> function? For example, a basic interpreter might >> define: >> >> type LNumber_Type is range 0..99_999; >> >> Can I declare.. >> >> for LNumber_Type'Image use LNumber_To_String; > However, it later says: > > [ARM 2005 13.3 (5/1)] > An attribute_designator is allowed in an attribute_definition_clause > only if this International Standard explicitly allows it .... > Finally, it should be checked if Image is explicitely allowed as an > attribute designator for an operational clause (I may check later to > give you a more formal answer to this one question). As others have suggested, probably not, or at best on an implementation basis only. At best, this suggests that this approach is unportable. >> Finally, there is actually a third question- more along >> the lines of "Should this language feature be used >> in this manner?", or is it preferable to just code your >> own along the lines of (which is what I presently use): >> >> function To_String(LNO : LNumber_Type) return String; > I would say, it is more handy to define a function, because a function > would be able to hold the exact formatting parameter your application > requires, it would be able to hold the exact optional defaults for > those parameters and it would better integrates with the overall > general design of an Ada application, that, “withing” package and > using renames clause. Using attribute, you are require to always use > thye type name as a prefix for such things as 'Image. True, but in my case I just needed the leading zeros, sans any sign: 900 to be displayed as "00900" (vs " 900"). > All of this providing I've understood what you were requesting for. Yep, you got it. Warren
From: Warren on 6 May 2010 16:05 Dmitry A. Kazakov expounded in news:10yarz51f24i9$.k5ouloeombf2$.dlg@ 40tude.net: > On Thu, 6 May 2010 17:10:20 +0000 (UTC), Warren wrote: > >> I have tried to google for this and have not yet found >> a suitable answer, so I'll troll, er, poll for an >> answer here.. >> >> Is there the ability to substitute your own S'Image >> function? For example, a basic interpreter might >> define: >> >> type LNumber_Type is range 0..99_999; >> >> Can I declare.. >> >> for LNumber_Type'Image use LNumber_To_String; >> >> If so, then the question is what the signature of >> the S'Image function looks like-- is it: >> >> function LNumber_To_String(LNO : LNumber_Type) return String; > > I am not sure what do you mean, but the following is legal Ada: > > generic > type T is private; > with function Image (X : T) return String; > package P is > ... > end P; > > type LNumber_Type is range 0..99_999; > > package PI is new P (LNumber_Type, LNumber_Type'Image); > > So attribute is a "plain" function with a clumsy name. I would never have though along those lines, but agree this isn't the "Right Thing"(T). Thanks
From: Robert A Duff on 6 May 2010 16:19
Warren <ve3wwg(a)gmail.com> writes: > As others have suggested, probably not, or at best on > an implementation basis only. At best, this suggests > that this approach is unportable. Definitely not, and not on an implementation-defined basis. An implementation may define its own attributes, and it can choose to make those user-specifiable, or not. But an implementation cannot make 'Image user-specifiable. Of course, an implementation can have a non-standard mode in which 'Image is user-specifiable. But in that mode, it's not an Ada implementation. > True, but in my case I just needed the leading zeros, sans > any sign: > > 900 to be displayed as "00900" (vs " 900"). So create a function called Image that does that. I think Image is a better name than To_String, by the way -- it's a common convention to use Image. The leading blank produced by T'Image is indeed annoying! What were they thinking?! Never mind, that's been discussed to death. It's not a huge problem, but it's one of the first things new Ada programmers notice, and it's a real turn-off. - Bob |