digitalmars.D.bugs - [Issue 2629] New: obj[n] not allowed for user-defined tuples
- d-bugmail puremagic.com (54/54) Jan 28 2009 http://d.puremagic.com/issues/show_bug.cgi?id=2629
- d-bugmail puremagic.com (9/9) Jan 28 2009 http://d.puremagic.com/issues/show_bug.cgi?id=2629
http://d.puremagic.com/issues/show_bug.cgi?id=2629 Summary: obj[n] not allowed for user-defined tuples Product: D Version: unspecified Platform: PC OS/Version: Linux Status: NEW Severity: enhancement Priority: P2 Component: DMD AssignedTo: bugzilla digitalmars.com ReportedBy: andrei metalanguage.com This is an annoying issue that makes tuples one order of magnitude less appealing than they might be. Currently, there is no literal to define type tuples but the TypeTuple supplants it: template TypeTuple(T...) { alias T TypeTuple; } Given: alias TypeTuple!(int, float) T; you can use its type members with T[0] and T[1]. Furthermore, creating a value of type T also works and allows you to access the members with t[0] and t[1]. There are some problems with tuple values, e.g. they can't be returned from functions: T fun() { T result; result[0] = 1; result[1] = 1.1; return result; // can't return a tuple } So then I created std.typecons.Tuple which has a field of type TypeTuple and various ways to get at it. The problem with that is that I can't reproduce the most desirable for getting fields: var[index]. What can be done is: (1) var.field[0], var.field[1] This is bad because these can't be functions; field must be exposed directly. Therefore, writing tuple proxies that use the same syntax is impossible. That turns out to be a major problem. (2) var.at!(0), var.at!(1) This is ugly and requires one to press shift a million times. The alternative var.at!0 works, but doesn't quite cut the mustard. (3) var._0, var._1 This is ugly too, and also needs to be complemented with one of (1) or (2) because it doesn't allow iteration with numbers. Never grew on me, and I've been using it for quite a while. So we'd want to allow var[0], var[1] etc. There are several possibilities of doing so, the simplest being CTFE: struct Tuple(T...) { private T field; ref T[i] opIndex(size_t i) { return field[i]; } } If you pass a compile-time index, the function should work. Right now it does only confuse the compiler :o). --
Jan 28 2009
http://d.puremagic.com/issues/show_bug.cgi?id=2629 andrei metalanguage.com changed: What |Removed |Added ---------------------------------------------------------------------------- Status|NEW |RESOLVED Resolution| |DUPLICATE *** This bug has been marked as a duplicate of 2628 *** --
Jan 28 2009