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Newsgroups: comp.lang.ada
Date: Wed, 7 Jul 2021 13:44:32 -0700 (PDT)
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Subject: Re: deferred constants
From: Shark8 <onewingedshark@gmail.com>
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Xref: reader02.eternal-september.org comp.lang.ada:62345
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On Wednesday, July 7, 2021 at 1:31:34 PM UTC-6, Matt Borchers wrote:
> Is it possible to define a constant in a package body that has it's initialization deferred to elaboration? 
> 
> For example... 
> 
> with Gnat.RegExp; 
> package body 
> pat : constant Gnat.RegExp.RegExp; 
> begin 
> pat := Gnat.RegExp.compile( "..." ); 
> end; 
> 
> Obviously it is not strictly necessary to create 'pat' as a constant, but it is ideal to define symbols as precise as possible. Without it being a constant, the compiler will obviously not check to make sure someone has not inadvertently overwritten it. 
> 
> GNAT gives me the following errors: 
> - constant declaration requires initialization expression 
> - deferred constant is frozen before completion 
> 
> The first error message is not true, but comes from the fact that the second IS true. Is there a way to postpone the freezing of a symbol until after elaboration?
Use RENAMES?

pat : Gnat.RegExp.RegExp renames Gnat.RegExp.compile( "..." );

Other than this, I would advise not using RegEx.