From: "Steve" <nospam_steved94@comcast.net>
Subject: Re: How to define an array of a variant record type?
Date: Tue, 18 Nov 2003 02:48:54 GMT
Date: 2003-11-18T02:48:54+00:00 [thread overview]
Message-ID: <qMfub.230787$Fm2.231960@attbi_s04> (raw)
In-Reply-To: BBDEBC6C.902D%office@anobject.net
To do this you must use a "default discriminant". In your record type
definition use:
type Name_Value( Value_Type : Name_Value_Type := String_Type ) is
...
There are a couple of other things you should be aware of.
1. When assigning values to the record, you can only change the type by
doing a complete record assignment.
That is:
Value : Name_Value;
Value := ( Value_Type => String_Type, --this is ok
String_Value => To_Unbounded_String( "Hello" );
Value.Value_Type := Integer_Type; -- will not work
Value := ( Value_Type => Integer_Type, -- ok
Integer_Value => 42 );
Value.Integer_Value := 43; -- ok
2. You can only change the discriminant through the record assignment if the
record was declared using the default.
That is:
Value : Name_Value(Integer_Type);
Value := ( Value_Type => String_Type, -- will not work.
String_Value => To_Unbounded_String( "Hello" );
Steve
(The Duck)
"Harald Schmidt" <office@anobject.net> wrote in message
news:BBDEBC6C.902D%office@anobject.net...
> Hi,
>
> I would like to define an array, which its element type is a variant
record
> and the Value_Type is only known at runtime.
>
> type Name_Value_Type is (String_Type,
> Integer_Type,
> Float_Type);
>
> type Name_Value(Value_Type : Name_Value_Type) is
> record
> The_Name : Unbounded_String;
> case Value_Type is
> when String_Type =>
> String_Value : Unbounded_String;
> when Integer_Type =>
> Integer_Value : Integer;
> when Float_Type =>
> The_Value : Float;
> end case;
> end record;
>
> type Name_Value_Sequence is array(Natural range <>) of Name_Value;
>
> The compiler says "unconstrained element type in array declaration",
> ...right!
>
> I know Ada is a strong typed language, but sometimes information is only
at
> runtime available. Does anyone know some workaround, or a regulare design
> pattern for this problem?
>
> Harald
>
>
>
next prev parent reply other threads:[~2003-11-18 2:48 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-11-17 16:57 How to define an array of a variant record type? Harald Schmidt
2003-11-17 17:35 ` Stephen Leake
2003-11-20 10:02 ` Craig Carey
2003-11-17 17:37 ` Marius Amado Alves
2003-11-18 2:48 ` Steve
2003-11-18 9:04 ` Marius Amado Alves
2003-11-17 18:45 ` Rodrigo Garcia
2003-11-18 2:48 ` Steve [this message]
2003-11-18 17:48 ` Nick Roberts
2003-11-19 2:38 ` Steve
2003-11-19 8:11 ` Preben Randhol
2003-11-19 13:26 ` Rodrigo Garcia
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