====== Type declarations ======
===== type_declaration =====
  * full_type_declaration
  * incomplete_type_declaration

===== Parents =====
  * entity_declarative_part
  * architecture_declarative_part
  * package
  * package_body
  * block_declarative_part
  * function_declarative_part
  * procedure_declarative_part
  * process_declarative_part

===== Further definitions =====
==== full_type_declaration ====
''type [[.:bnf#identifier]] is [[.:bnf#type_definition]] ;''

==== incomplete_type_declaration ====
''type [[.:bnf#identifier]] ;''

===== Examples =====
Two Integer types //A// and //B//, both of which have a range of 1 to 10, are declared.
<code vhdl>
TYPE A IS RANGE 1 TO 10 ;
TYPE B IS RANGE 1 TO 10 ;
</code>

----

The physical type //capacitance// is declared as a Real-type with a range of 0 to 1E16. Afterwards a base unit and units derived from it are declared.
<code vhdl>
TYPE capacitance IS RANGE 0 TO 1E16
   UNITS
      fF ; -- Femtofarad
      pF = 1000 fF ;  -- Picofarad
      nF = 1000 pF ;  -- Nanofarad
      uF = 1000 nF ;  -- Microfarad
   END UNITS ;
</code>

----

A recursive structure is created. At first type //cell// is declared incompletely. As a consequence the access type //link// is declared on the type //cell// .

Afterwards type //cell// is declared completely as Record. The elements //succ// and //pred// are declared as index types. By doing so an interlinked list can be created in which every element receives an index to both its predecessor and its successor.
<code vhdl>
TYPE cell ;

TYPE link IS ACCESS cell ;

TYPE cell IS
   RECORD
      value : integer ;
      succ : link ;
      pred : link ;
   END RECORD ;
</code>

----

These are examples of standard predefined types. //boolean// , //bit// and //character// are enumeration types.

//string// and //bit_vector// are arrays which can have any width (RANGE <>) with the maximum width being determined by the corresponding type ( //positive// , //natural// ).
<code vhdl>
TYPE boolean IS ( false, true ) ;

TYPE bit IS ( '0', '1' ) ;

TYPE string IS ARRAY (positive
      RANGE <>) OF character ;
TYPE bit_vector IS ARRAY
      (natural RANGE <>) OF bit ;
</code>