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From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Rough proposal to make some generic types static
Date: Tue, 22 Jul 2014 00:43:42 +0300
Organization: Tidorum Ltd
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Xref: news.eternal-september.org comp.lang.ada:21103
Date: 2014-07-22T00:43:42+03:00
List-Id: <comp.lang.ada>

On 14-07-22 00:32 , Victor Porton wrote:
> Niklas Holsti wrote:
> 
>> On 14-07-21 23:54 , Victor Porton wrote:
>>> Victor Porton wrote:
>>>
>>>> What in the RM signifies that Enum_Type (below) is not a static scalar
>>>> type?
>>
>> (Just as a reminder: Enum_Type is a formal type in a generic:
>>
>>    generic
>>       type Enum_Type is (<>);
>>    ...
>> )
>>
>>> I've found: RM 4.9 26/3:
>>>
>>> "A static scalar subtype is an unconstrained scalar subtype whose type is
>>> not a descendant of a formal type, or ..."
>>>
>>> Why this rule? Can it be relaxed?
>>
>> As I understand it, this rule (and others similar to it) allow compilers
>> to create "shared code" generics, that is, to compile a generic unit
>> into a single set of machine code that works for all instances of the
>> generic, thus reducing code size at the cost of possibly increasing
>> execution time.
> 
> Really?

Yes.

> How a compiler may create shared code when a formal scalar type may 
> be of different sizes in different instantiations?

Perhaps Randy Brukardt can explain how Janus/Ada does it.

There used to be other code-sharing Ada compilers -- TLD-Ada for the
MIL-1750 processors comes to mind -- but as the memory sizes available
in embedded systems increased, the "macro generic" approach became more
popular.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
      .      @       .