light weight types
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From: Michal Kleczek on 29 Sep 2009 16:52 Tom Anderson wrote: > On Tue, 29 Sep 2009, Michal Kleczek wrote: > >> Tom Anderson wrote: >>> If you want to be able to have arbitrary units which can be checked at >>> compile-time, sure, you need to add difficult stuff to the language. If >>> you can satisfy yourself with a fixed set of units, or runtime-only >>> checking, you can do it in java now. >> >> Fixed set of units is problematic because it is... fixed :) >> Runtime-only checking is actually no checking at all (who cares if a bug >> manifests itself in an IllegalArgumentException or otherwise?) > > Because that's going to be a lot more obvious during testing than a value > being silently wrong. > There is no real difference. Testing would find that the value is wrong anyway. And the value IS wrong - otherwise you wouldn't get the exception. The only difference is that it can somewhat help finding the root cause. -- Michal
From: Arne Vajhøj on 29 Sep 2009 21:56 Lew wrote: > Michal Kleczek wrote: >> 2. First class type parameters ( "new T()" anybody? :) ) > > No, thanks. I think it would be nice to have. And so natural that it would not add to the complexity of the language. Arne
From: Arne Vajhøj on 29 Sep 2009 21:57 Joshua Cranmer wrote: > On 09/29/2009 03:35 PM, Michal Kleczek wrote: >> 2. First class type parameters ( "new T()" anybody? :) ) > > What would happen if T were an interface or abstract? Better yet, what > if it were a wildcard type parameter? Obviously it would need to be a restriction that T is known to have a parameter less constructor. It works in C#. Arne
From: Mike Amling on 29 Sep 2009 23:24 Roedy Green wrote: > Consider a program that uses a mixture of 10-character and 13-digit > ISBN numbers (International Standard Book Number). From Java's point > of view, they are all Strings. > > It would be nice if there were some mechanism to label Strings with a > light-weight type, probably a purely compile-time concept, similar to > generics. You would then label some string vars as ISBN13 and some as > ISBN10, and similarly parameters to methods. Then the compiler could > detect an improper passing of in ISBN13 string to an ISBN10 parameter. You could define classes ISBN10 and ISBN13. > > An extension of this idea is units of measure, so that you could not > pass a cm variable to an inch parameter (though possibly you could > with an automatic conversion applied). > > Think how many times you have wondered if a variable is measured in > seconds, ms, or ns. Here would be a formal way to specify and check > your assumption was correct. > > Going a step further, your type might have a associated assertion to > make sure the value were valid. Perhaps there would be a way to > insert that assertion at every assignment. Surely someone somewhere must have something like this already, with classes or interfaces for time, distance, mass, etc. --Mike Amling
From: Kevin McMurtrie on 30 Sep 2009 01:23
In article <4ac1b9d1$0$21087$ec3e2dad(a)unlimited.usenetmonster.com>, "Kenneth P. Turvey" <evoturvey(a)gmail.com> wrote: > On Mon, 28 Sep 2009 23:25:39 -0700, Kevin McMurtrie wrote: > > > In article <alpine.DEB.1.10.0909282318480.8778(a)urchin.earth.li>, > > Tom Anderson <twic(a)urchin.earth.li> wrote: > > > >> On Mon, 28 Sep 2009, Michal Kleczek wrote: > >> > >> > Roedy Green wrote: > >> > > >> >> Consider a program that uses a mixture of 10-character and 13-digit > >> >> ISBN numbers (International Standard Book Number). From Java's point > >> >> of view, they are all Strings. > >> >> > >> >> It would be nice if there were some mechanism to label Strings with > >> >> a light-weight type, probably a purely compile-time concept, similar > >> >> to generics. You would then label some string vars as ISBN13 and > >> >> some as ISBN10, and similarly parameters to methods. Then the > >> >> compiler could detect an improper passing of in ISBN13 string to an > >> >> ISBN10 parameter. > >> >> > >> >> An extension of this idea is units of measure, so that you could not > >> >> pass a cm variable to an inch parameter (though possibly you could > >> >> with an automatic conversion applied). > >> >> > >> >> Think how many times you have wondered if a variable is measured in > >> >> seconds, ms, or ns. Here would be a formal way to specify and check > >> >> your assumption was correct. > >> > >> Gosling keeps talking about adding this to java. > >> > >> > That is not so easy to make it right. Read for example: > >> > http://research.sun.com/projects/plrg/Publications/p109-allen.pdf > >> > >> If you want to be able to have arbitrary units which can be checked at > >> compile-time, sure, you need to add difficult stuff to the language. If > >> you can satisfy yourself with a fixed set of units, or runtime-only > >> checking, you can do it in java now. > >> > >> tom > > > > Hopefully nobody 'solves' this by adding Generics to Strings. Java's > > syntax is already going off the deep end. (And yet the simple things > > like unsigned math and arrays of contiguous Object data are dismissed as > > not worth the effort.) > > Both of those are real annoyances... I've got one more though, closures. > Anonymous classes are ugly when unneeded. That too. MacOS 10.6 now uses them for lightweight parallel code execution. Java has the Future and Callable classes but they're clumsy. -- I will not see your reply if you use Google. |