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October 19, 2007 [Issue 1597] New: It is not possible to specialize template on associative array. | ||||
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http://d.puremagic.com/issues/show_bug.cgi?id=1597 Summary: It is not possible to specialize template on associative array. Product: D Version: 1.022 Platform: All OS/Version: All Status: NEW Severity: enhancement Priority: P2 Component: DMD AssignedTo: bugzilla@digitalmars.com ReportedBy: aarti@interia.pl void parse(T)() { } //What to write here??? void parse(T : ?????)() { } void main() { Â Â Â parse!(int[char[]])(); } -- |
October 19, 2007 [Issue 1597] It is not possible to specialize template on associative array. | ||||
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Posted in reply to d-bugmail | http://d.puremagic.com/issues/show_bug.cgi?id=1597 ------- Comment #1 from aarti@interia.pl 2007-10-19 17:32 ------- Also syntax of matching for normal arrays is cryptic. It would be better to have following syntax for matching arrays: void parse(T : E[])() {} which is much more clear (match types which are collections of elements of type E). Similarly some cleanups could be done in is() expression for types. proposed syntax for associative arrays: void parse(T : V[K])() {} Related proposal from Bill Baxter: http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D.learn&article_id=9858 -- |
October 19, 2007 [Issue 1597] It is not possible to specialize template on associative array. | ||||
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Posted in reply to d-bugmail | http://d.puremagic.com/issues/show_bug.cgi?id=1597 ------- Comment #2 from andrei@metalanguage.com 2007-10-19 17:35 ------- While acknowledging this as a bug in the language, below is a fix for the time being: import std.stdio; void parse(T, U = void, V = void)() { writeln("Wuddever"); } void parse(T : U[V], U, V)() { writeln("Hash"); } void main() { parse!(int[char[]])(); parse!(int[])(); parse!(int)(); } The second suggestion: void parse(T : E[])() {} won't work because it's unclear whether E is a newly-introduced symbol ("must be inferred") or a previously-defined symbol ("must be E that I defined in this module"). -- |
October 19, 2007 Re: [Issue 1597] It is not possible to specialize template on associative array. | ||||
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Posted in reply to d-bugmail | > The second suggestion:
>
> void parse(T : E[])() {}
>
> won't work because it's unclear whether E is a newly-introduced symbol
> ("must be inferred") or a previously-defined symbol ("must be E that I
> defined in this module").
Probably your are right :-) That was more pointing problem, that proposing real solution. Maybe some kind of suggestion.
But in other hand probably you will admit that current solution:
void parse(T : T[])
is even worse?
Inside function you get something completely different than you put when instantiating template. Inside function T means element of array, while it is instantiated as T[].
PS. It seems that best way to talk with Andrei is to submit bug :D
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October 19, 2007 [Issue 1597] It is not possible to specialize template on associative array. | ||||
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Posted in reply to d-bugmail | http://d.puremagic.com/issues/show_bug.cgi?id=1597 ------- Comment #3 from wbaxter@gmail.com 2007-10-19 17:52 ------- (In reply to comment #2) > won't work because it's unclear whether E is a newly-introduced symbol ("must > be inferred") or a previously-defined symbol ("must be E that I defined in this > module"). What's wrong with the C++ way of specifying specializations? Just void parse(T[])() {} -- |
October 19, 2007 [Issue 1597] It is not possible to specialize template on associative array. | ||||
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Posted in reply to d-bugmail | http://d.puremagic.com/issues/show_bug.cgi?id=1597 ------- Comment #4 from andrei@metalanguage.com 2007-10-19 18:04 ------- (In reply to comment #3) > (In reply to comment #2) > > won't work because it's unclear whether E is a newly-introduced symbol ("must > > be inferred") or a previously-defined symbol ("must be E that I defined in this > > module"). > > What's wrong with the C++ way of specifying specializations? > Just > void parse(T[])() {} > It has the same problem. Consider: // wanna specialize on hashes, and also pattern match T and U! Cool! void parse(T[U])() {} Now if the same module adds or imports a type called U, a bad time is being had. -- |
October 19, 2007 [Issue 1597] It is not possible to specialize template on associative array. | ||||
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Posted in reply to d-bugmail | http://d.puremagic.com/issues/show_bug.cgi?id=1597 ------- Comment #5 from aarti@interia.pl 2007-10-19 18:19 ------- (In reply to comment #2) But in other hand probably you will admit that current solution: void parse(T : T[]) is even worse? Inside function you get something completely different than you put when instantiating template. Inside function T means element of array, while it is instantiated as T[]. So maybe: void parse(T : auto E[]) {} and void parse(T : auto V[K]) {} to say that these symbols are inferred? -- |
October 19, 2007 [Issue 1597] It is not possible to specialize template on associative array. | ||||
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Posted in reply to d-bugmail | http://d.puremagic.com/issues/show_bug.cgi?id=1597 ------- Comment #6 from andrei@metalanguage.com 2007-10-19 18:35 ------- (In reply to comment #5) > (In reply to comment #2) > But in other hand probably you will admit that current solution: > void parse(T : T[]) > > is even worse? > > Inside function you get something completely different than you put when instantiating template. Inside function T means element of array, while it is instantiated as T[]. That's very ugly but Walter cannot be convinced to give it up. > So maybe: > void parse(T : auto E[]) {} and > void parse(T : auto V[K]) {} > to say that these symbols are inferred? This idea has been iterated a number of times. In the end, there was admission that the current syntax of appending the symbols to the list is as good as any other. -- |
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