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digitalmars.D.learn - enum-indexed arrays

reply =?UTF-8?B?Ik5vcmRsw7Z3Ig==?= <per.nordlow gmail.com> writes:
Have anybody thought about adding safe enum-based indexing to 
builtin arrays? Ada has this.

IMHO I believe this could be implemented either in the compiler, 
druntime or phobos.

Example

     enum I { a=3,b=4,c=5 }
     int[I] x = [3,4,5];
     assert(x[I.a] == 3);
     assert(x[I.b] == 4);
     assert(x[I.c] == 5);

Iteration through

     foreach (i, e; x) {}

where

i is of type I

and

e is of type int
Sep 20 2014
parent reply "bearophile" <bearophileHUGS lycos.com> writes:
Nordlöw:


 Have anybody thought about adding safe enum-based indexing to 
 builtin arrays? Ada has this.


I'd like this. I'd like even more: a general way to have 
optionally strongly typed array indexes.



     enum I { a=3,b=4,c=5 }
     int[I] x = [3,4,5];


In D currently that "int[I]" is an associative array with I index 
and int values. So in another post I have suggested another 
syntax.

Bye,
bearophile
Sep 20 2014
parent reply =?UTF-8?B?Ik5vcmRsw7Z3Ig==?= <per.nordlow gmail.com> writes:
On Saturday, 20 September 2014 at 20:43:28 UTC, bearophile wrote:

 In D currently that "int[I]" is an associative array with I 
 index and int values. So in another post I have suggested 
 another syntax.


Couldn't we simply add an optimization pass that CT-introspects 
the enumerators of an enum-indexed AA and represent it internally 
as a lookup-table if the enumerator values are adjacent (enough)?
Sep 20 2014
parent reply =?UTF-8?B?Ik5vcmRsw7Z3Ig==?= <per.nordlow gmail.com> writes:
On Saturday, 20 September 2014 at 21:05:12 UTC, Nordlöw wrote:

 On Saturday, 20 September 2014 at 20:43:28 UTC, bearophile 
 wrote:

 In D currently that "int[I]" is an associative array with I 
 index and int values. So in another post I have suggested 
 another syntax.


 Couldn't we simply add an optimization pass that CT-introspects 
 the enumerators of an enum-indexed AA and represent it 
 internally as a lookup-table if the enumerator values are 
 adjacent (enough)?


Further it would be nice if the newly added std.range.enumerate 
got support for Enumerator being an enum when instantiated with 
an enum-indexed array.

Currently it fails, for starters, because the default value of 
second parameter

     Enumerator start = 0

should be

     Enumerator start = Enumerator.min

in the case when Enumerator is an enum.
Sep 20 2014
parent reply "bearophile" <bearophileHUGS lycos.com> writes:
Nordlöw:


 should be

     Enumerator start = Enumerator.min


This also requires the enum to have adjacent values (in general 
enums can skip values).

Bye,
bearophile
Sep 20 2014
parent reply "Baz" <basile.burg gmx.com> writes:
On Saturday, 20 September 2014 at 22:00:24 UTC, bearophile wrote:

 Nordlöw:


 should be

    Enumerator start = Enumerator.min


 This also requires the enum to have adjacent values (in general 
 enums can skip values).

 Bye,
 bearophile


Not true, because you can use std.traits.EnumMembers to prepare 
an enum member rank lookup table, so that values have even not be 
consecutive.

there is an example here:
http://dlang.org/phobos/std_traits.html#EnumMembers

and a concret application in this personal project (e.g line 111):
https://github.com/BBasile/bitSet/blob/master/import/bitsets/bitsets.d
Sep 20 2014
parent =?UTF-8?B?Ik5vcmRsw7Z3Ig==?= <per.nordlow gmail.com> writes:
On Saturday, 20 September 2014 at 22:13:30 UTC, Baz wrote:

 Not true, because you can use std.traits.EnumMembers to prepare 
 an enum member rank lookup table, so that values have even not 
 be consecutive.


You're correct. Even better not having that limitation :)


 there is an example here:
 http://dlang.org/phobos/std_traits.html#EnumMembers

 and a concret application in this personal project (e.g line 
 111):
 https://github.com/BBasile/bitSet/blob/master/import/bitsets/bitsets.d


Nice!
Sep 20 2014