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From: "REH" <me@you.com>
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Subject: Re: Type safety, C++ and code generation
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Date: Sun, 30 Apr 2006 15:23:46 GMT
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<adaworks@sbcglobal.net> wrote in message 
news:o%35g.64094$_S7.49734@newssvr14.news.prodigy.com...
>
> "Maciej Sobczak" <no.spam@no.spam.com> wrote in message 
> news:e2qn8t$n13$1@sunnews.cern.ch...
>>
>> What about making different types really distinct?
>>
>> typedef ranged_type<int, 0, 100> R1;
>> typedef ranged_type<int, 0, 100> R2;
>> typedef ranged_type<int, 0, 101> R3;
>>
>>
>> Above, R1 and R2 are *equal* to the compiler, but R3 is distinct from the 
>> other two.
> This example raises the issue of structural equivalence versus
> name equivalence.  In Ada R1 and R2 would not be
> equivalent.
>
> Ada is designed for name equivalence.    Most other languages
> are designed for structural equivalence.    In this respect, Ada
> continues to be just a wee bit more type safe than languages
> designed for structural equivalence.
>
> Richard Riehle

C++ does not use structural equivalence (nor does C).  It too uses name 
equivalence.  The problem is that typedef does not introduce a new name, but 
an alias.  The only way to introduce a new name is via enum, struct, class, 
or union.  templates also introduce new names, but instantiation with the 
same set of parameters are of the same name.  structs defined with the exact 
same fields but different names, are different.

REH