digitalmars.D.bugs - [Issue 481] New: Letting compiler determine length for fixed-length arrays
- d-bugmail puremagic.com Nov 04 2006
- d-bugmail puremagic.com Nov 26 2010
- d-bugmail puremagic.com Nov 26 2010
- d-bugmail puremagic.com Dec 03 2010
- d-bugmail puremagic.com Dec 11 2010
- d-bugmail puremagic.com Dec 14 2010
- d-bugmail puremagic.com Dec 14 2010
http://d.puremagic.com/issues/show_bug.cgi?id=481 Summary: Letting compiler determine length for fixed-length arrays Product: D Version: 0.172 Platform: All OS/Version: All Status: NEW Severity: enhancement Priority: P2 Component: DMD AssignedTo: bugzilla digitalmars.com ReportedBy: wbaxter gmail.com There needs to be a way to tell the compiler to count up how many elements there are in a fixed length array. In C++ you use empty brackets, [], but in D this means "create a dynamic array". Sometimes you want a fixed-length array but it's a pain to count up the elements by hand. The main example is embedding binary data, like images, into the program as code. A possible syntax would be to use the pre-existing '$' or 'length' indicators to specify that the length of the array should be the length of the initializer: int arr[$] = [1,2,3,4]; // makes an int[4] int arr[length] = [1,2,3,4]; // ditto int[$] arr = [1,2,3,4]; // ditto int[length] arr = [1,2,3,4]; // ditto Another option would be to re-use the keyword auto. int arr[auto] = [1,2,3,4]; // makes an int[4] int[auto] arr = [1,2,3,4]; // ditto Using 'auto' makes sense in that the length really is part of the type of a fixed-length array, so really what you're saying is "automatically deduce just this part of the type for me". Using 'auto' would also be extend naturally to associative arrays when/if there are initializers for those. For example: int[auto] str_to_num = [ "one":1, "two":2, "three":3 ]; This would specify that value type is int, but let the key type be automatically deduced from the initializer. --
Nov 04 2006
d-bugmail puremagic.com http://d.puremagic.com/issues/show_bug.cgi?id=481 Andrei Alexandrescu <andrei metalanguage.com> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|NEW |ASSIGNED CC| |andrei metalanguage.com AssignedTo|nobody puremagic.com |bugzilla digitalmars.com --- Comment #1 from Andrei Alexandrescu <andrei metalanguage.com> 2010-11-26 11:36:34 PST --- This enhancement's importance is raised by the fact that array literals have dynamic length by default, so simply writing auto a = [1,2,3,4]; won't make a of type int[4]. I think using "[$]" is the most sensible option. The special meaning of "length" inside array brackets needs to be eliminated anyway, and "[auto]" may confuse people into thinking it's an associative array. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Nov 26 2010
http://d.puremagic.com/issues/show_bug.cgi?id=481 bearophile_hugs eml.cc changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |bearophile_hugs eml.cc --- Comment #2 from bearophile_hugs eml.cc 2010-11-26 12:24:55 PST --- I agree that this syntax is good: int[$] arr = [1,2,3,4]; But it solves only half of the problem. Currently this compiles: int[4] a = [1, 2, 3]; void main() {} While this generates: object.Exception: lengths don't match for array copy void main() { int[4] a = [1, 2, 3]; } They are two different situations. But they don't look different, the first just look like a special case. To solve the second half of the problem someone has suggested this syntax that looks good enough: int[4] a = [1, 2, 3, ...]; a[3] is filled with typeof(a[0]).init. For more info see bug 3849 -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Nov 26 2010
http://d.puremagic.com/issues/show_bug.cgi?id=481 Bruno Medeiros <bdom.pub+deebugz gmail.com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |bdom.pub+deebugz gmail.com --- Comment #3 from Bruno Medeiros <bdom.pub+deebugz gmail.com> 2010-12-03 05:28:18 PST --- (In reply to comment #1)This enhancement's importance is raised by the fact that array literals have dynamic length by default, so simply writing auto a = [1,2,3,4]; won't make a of type int[4]. I think using "[$]" is the most sensible option.
I don't quite get this argument. If you have a syntax such as "[$]" (I assume you are referring to Bill's example of "int[$] arr"), then obviously auto a = [1,2,3,4]; still won't make a of type int[4]... The only way to use auto (in it current form) to declare a static array would be to have a syntax for a static array literal. Or to have a template and/or function to create the static array value. Isn't this latter alternative preferable? A bit more verbose, but no language changes should be necessary. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Dec 03 2010
http://d.puremagic.com/issues/show_bug.cgi?id=481 --- Comment #4 from bearophile_hugs eml.cc 2010-12-11 00:35:09 PST --- (In reply to comment #3)I don't quite get this argument.
Originally array literals used to create fixed length arrays: auto a = [1,2,3,4]; ==> int[4] Later D was changed so that line creates a dynamic array: auto a = [1,2,3,4]; ==> int[] that's handy, but now if you have a long array literal and you want a fixed-sized array you have to count how many items it has. This is not handy, especially if later you want to add or remove items from the array literal (in the source code). It's not handy also because if by mistake you write a bigger number, empty items are silently created (but only for global fixed-sized literals): int[5] a = [1,2,3,4]; ==> int[5] So Bill and others have suggested a simple syntax that is easy enough to read, understand and remember: int[$] a = [1,2,3,4]; ==> int[4] And to avoid bugs produced by wrong number of items a second syntax may be introduced, that makes it explicit that there are some auto initialized items: int[6] a = [1,2,3,4,...]; ==> int[6] -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Dec 11 2010
http://d.puremagic.com/issues/show_bug.cgi?id=481 --- Comment #5 from Bruno Medeiros <bdom.pub+deebugz gmail.com> 2010-12-14 04:27:54 PST --- (In reply to comment #4)(In reply to comment #3)I don't quite get this argument.
Originally array literals used to create fixed length arrays:
Yes, I understood the use case for this problem, and how the [$] syntax would solve the limitation in a way. But then we're not looking for a syntax that would also allows us to use auto (as in "auto a = [1,2,3,4];"), is that what we're saying? -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Dec 14 2010
http://d.puremagic.com/issues/show_bug.cgi?id=481 --- Comment #6 from bearophile_hugs eml.cc 2010-12-14 13:24:26 PST --- (In reply to comment #5)But then we're not looking for a syntax that would also allows us to use auto (as in "auto a = [1,2,3,4];"), is that what we're saying?
Now I think I understand what you mean. You mean something like: auto[$] a = [1,2,3,4]; ==> int[4] So auto lets the D compiler infer the element type and count the items, but the result is a fixed-length array still. I think this case is not common enough to deserve a third syntax. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Dec 14 2010