Re: String indexing again

[HyperHacker <hyperhacker@...>]

On Mon, Dec 20, 2010 at 14:27, Axel Kittenberger <axkibe@gmail.com> wrote:
> "A string that doesnt support indexing"
>
> sorry that should read,
>
> "An array that doesnt support indexing"
>
> On Mon, Dec 20, 2010 at 10:26 PM, Axel Kittenberger <axkibe@gmail.com> wrote:
>> This
>>
>>> --s[n] returns string, you want value:
>>> The former case seems more convenient and cleaner;
>>
>> conflicts with thihs:
>>
>>> In Lua as
>>> well sometimes a string will not contain text, but just function as an
>>> array of bytes read from/written to a binary file. (This is perhaps
>>> another argument for allowing indexing?)
>>
>> Since then an index should return a byte.
>>
>> To refer to the OP, if you shoot at the manual, I'd go for this
>> sentence, In 2.2 "String represents arrays of characters.". A string
>> that doesnt support indexing, [] in other languages called "the array
>> operator" is an oxymoron. Would better say, "String represts
>> _sequences_ of bytes. (signed or unsigned, what I see Lua code
>> converts between (char) and (unsigned char) depending on context forth
>> and back). Also Lua doesnt know about "chars".
>>
>> You are right. Strings are not necessarily text or an array of
>> characters, since they are also used for binary data. In that case
>> they are more a interned "binary object". I also agree
>> force-converting everything to one format like PHP isn't a good idea.
>>
>> And looking at strings with dynamic sized chars, and binary data, the
>> workings of the index method should be different for both - another
>> argument against a standard index default.
>>
>> Somehow I wish, one could change the metatable of a particular string,
>> or a kind of strings. Instead of one metatable for all strings... But
>> I suppose aside from implementation this conflicts from concept
>> already with interning.
>>
>>> Also maybe worth considering: Should files allow numeric indexing,
>>> treating them as giant on-disk byte arrays? I usually wrap mine in a
>>> metatable that does just that; e.g. f[3] = 3rd byte of file.
>>
>> Not all files are seekable. (Especially e.g. the Linux notion of
>> character devices as files)
>>
>
>

> This
>
> > --s[n] returns string, you want value:
> > The former case seems more convenient and cleaner;
>
> conflicts with thihs:
>
> > In Lua as
> > well sometimes a string will not contain text, but just function as an
> > array of bytes read from/written to a binary file. (This is perhaps
> > another argument for allowing indexing?)
>
> Since then an index should return a byte.
Well, it returns a byte either way; you just need to use :byte() to
get the numeric value.

> Somehow I wish, one could change the metatable of a particular string,
> or a kind of strings.
You can, as people suggested earlier, wrap strings in an object with
its own metatable:
function myString(str) return setmetatable({_str = str} {...}) end
s = myString "hello"

-- 
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