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Newsgroups: comp.lang.ada
Date: Thu, 9 May 2013 09:12:41 -0700 (PDT)
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Subject: Re: User defined type conversion
From: Shark8 <onewingedshark@gmail.com>
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Date: 2013-05-09T09:12:41-07:00
List-Id: <comp.lang.ada>

Here's two ways to do it:

    type AB is tagged
	record
	    A, B : Unsigned_16;
	end record;

    type abcd is tagged
	record
	    a,b,c,d: Unsigned_8;
	end record;

    ----------------------------------------------
    
    Function Convert(Input : AB) Return abcd is
	-- Note, these records could have dummy variables and layout
	-- clauses to exactly match the tagged-record's fields.
	type ut_AB is record
	    A, B : Unsigned_16;
	end record;

	type ut_abcd is record
	    a,b,c,d: Unsigned_8;
	end record;
	
	Function Convert is new unchecked_conversion
	  ( source => ut_AB, target => ut_abcd);
	
	-- Here we overlay the non-tagged record atop the tagged 
	-- record's fields.
	Working : ut_ab
	  with import, convention => Ada, address => input.A'Address;
    begin
	Return Result : abcd do
	    declare
		Result_Subsection : ut_abcd
		  with Import, Convention => Ada, Address => Result.A'Address;
	    begin
		-- Apply the conversion.
		Result_Subsection:= Convert(working);
	    end;
	end return;
    end Convert;

    -- This is safer than the above.
    Function Convert_Fields(Input : AB) Return abcd is
	Function High( Input : Unsigned_16 ) Return Unsigned_8 is
	begin
	    Return Unsigned_8(Shift_Right(Input, 8));
	end High;
	
	Function Low( Input : Unsigned_16 ) Return Unsigned_8 is
	begin
	    Return Unsigned_8( 16#00FF# and Input );
	End Low;
	
	A : Unsigned_8 renames High	( Input.A );
	B : Unsigned_8 renames Low	( Input.A );
	C : Unsigned_8 renames High	( Input.B );
	D : Unsigned_8 renames Low	( Input.B );
	
    begin
	Return ( A, B, C, D );
    End Convert_Fields;