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Re: How do I set this type variable?

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On 09/18/16 05:47 PM, supercat@casperkitty.com wrote:
> On Saturday, September 17, 2016 at 7:19:21 PM UTC-5, Malcolm McLean wrote:
>> You have two policies. One is "const correctness", whereby everything
>> is const unless the function actually needs to change it. The
>> other is rigorous elimination and deprecation of const as an
>> undesirable programming construct.
>>
>> The problems are created in between.
>
> Many programming languages fail to recognize the concepts of a readable
> pointer, a read-only pointer, and a pointer to an immutable object.  All
> three of them could be characterized as a "SomeType const *", but they
> should have distinct meanings.
>
> Some libraries accept pointers from client code and later give those same
> pointers back to client code.  The libraries won't write through the
> pointers, but won't care if client code does so with the originals or the
> passed-back copies.  Such pointers should be "readable".
>
> Some libraries accept pointers from client code and pass them on to other
> code, and the copies of the pointers should never be written through.  The
> supplier of the pointers, however, may retain the right to write through
> them, especially after the called function returns.  Such pointers should
> be "read-only".
>
> Some libraries may cache information read through pointers they receive,
> and may malfunction if any code ever writes through them.  The targets of
> such pointers should be "immutable".
>
> Some ambiguities with pointer qualifiers could be resolved by having a
> "return" qualifier, such that e.g.
>
>      char *strchr(char return const *src, int match);
>
> would indicate that if the first past argument has a const qualifier,
> the return value should be regarded as having one also, but if the
> source argument does not have one, the return value shouldn't either.
> Had such a qualifier been available when strchr was defined, that would
> have avoided a lot of difficulties with functions like strchr.  It would
> not solve all such difficulties, especially in cases where a library
> needs to store passed-in pointers between function calls, but it would
> have helped many.

Function overloading is a more elegant solution for this.

-- 
Ian

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How do I set this type variable? Thiago Adams <thiago.adams@gmail.com> - 2016-09-16 13:08 -0700
  Re: How do I set this type variable? BartC <bc@freeuk.com> - 2016-09-16 21:40 +0100
    Re: How do I set this type variable? Thiago Adams <thiago.adams@gmail.com> - 2016-09-16 13:57 -0700
      Re: How do I set this type variable? Thiago Adams <thiago.adams@gmail.com> - 2016-09-16 14:07 -0700
      Re: How do I set this type variable? jacobnavia <jacob@jacob.remcomp.fr> - 2016-09-16 23:32 +0200
        Re: How do I set this type variable? Thiago Adams <thiago.adams@gmail.com> - 2016-09-17 12:05 -0700
          Re: How do I set this type variable? BartC <bc@freeuk.com> - 2016-09-17 20:46 +0100
    Re: How do I set this type variable? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-09-17 17:19 -0700
      Re: How do I set this type variable? supercat@casperkitty.com - 2016-09-17 22:47 -0700
        Re: How do I set this type variable? luser droog <luser.droog@gmail.com> - 2016-09-18 13:44 -0700
        Re: How do I set this type variable? Ian Collins <ian-news@hotmail.com> - 2016-09-19 17:00 +1200
          Re: How do I set this type variable? David Brown <david.brown@hesbynett.no> - 2016-09-19 09:34 +0200
            Re: How do I set this type variable? supercat@casperkitty.com - 2016-09-19 08:18 -0700
  Re: How do I set this type variable? Richard Damon <Richard@Damon-Family.org> - 2016-09-23 12:07 -0400
    Re: How do I set this type variable? Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-23 11:57 -0700

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