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Newsgroups: comp.lang.ada
Date: Wed, 7 Jul 2021 12:31:33 -0700 (PDT)
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Subject: deferred constants
From: Matt Borchers <mattborchers@gmail.com>
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Xref: reader02.eternal-september.org comp.lang.ada:62340
List-Id: <comp.lang.ada>

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?