Description
Lets you give an alternative name for almost anything. Particularly useful for renaming a slice of an array, as it avoids the need to define a new signal or variable. Also allows one package to inherit procedures and functions from another package by aliasing them.
Formal Syntax
alias AliasName [: Datatype] is Name [Signature];
Signature = [TypeName, ...] return TypeName
Placement
PACKAGE Pack IS
... 
END PACKAGE Pack;
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PACKAGE BODY Pack IS
...
END PACKAGE BODY Pack;
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Blk:BLOCK
...
BEGIN
...
END BLOCK Blk;
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ENTITY Ent IS
...
BEGIN
...
END ENTITY Ent;
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ARCHITECTURE Arc OF Ent IS
...
BEGIN
...
END ARCHITECTURE Arc;
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CONFIGURATION Conf OF Ent IS
...
END CONFIGURATION Conf;
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Proc:PROCESS(...)
...
BEGIN
...
END PROCESS Proc;
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PROCEDURE P(...) IS
...
BEGIN
...
END PROCEDURE P;
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FUNCTION F(...) RETURN Tp IS
...
BEGIN
...
END FUNCTION F;
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Rules
The AliasName may be an identifier, character or operator. An aliased procedure, function or enumeration literal must be identified unambiguously by a signature, which identifies the parameter types and return type (to allow for overloading).
Things to remember
The DataType and the Name being aliased must both be static, so an aliased slice name must have a static index constraint.
Synthesis
Not supported by many synthesis tools.
Example
function F (A, B: Std_logic_vector) return BOOLEAN is
alias P1: Std_logic_vector(1 to A'LENGTH) is A;
alias P2: Std_logic_vector(1 to B'LENGTH) is B;
-- Alias is used to create 2 local vectors with the same range
begin
for I in P1'RANGE loop
if P1(I) = P2(I) then
...
alias ">" is
F[Std_logic_vector, Std_logic_vector] return BOOLEAN;
See Also
Constant
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