On Wed, 8 Jan 2014, Howard Page-Clark wrote:
On 08/01/2014 20:01, Sven Barth wrote:
On 08.01.2014 19:40, Howard Page-Clark wrote:
On 08/01/2014 18:16, Jürgen Hestermann wrote:
Today I found this type definition in some FreePascal sources:
TypeReal =type Double;
I wondered what the second “type” keyword means here (I have never seen
this before).
You are being rather obtuse.
Ignore the diagrams in the docs if they don't help you.
The double use of type here simply means that the "Real" type is being
defined as an alias for double. The two type identifiers now mean
exactly the same thing as the "=" indicates.
No, an alias would be
=== code begin ===
type
Real = Double;
=== code end ===
Using the "type" behind the "=" tells the compiler to declare a new type
based on the right side. So a "Double" and a "Real" are not assignment
compatible and can have different sets of operator overloads.
That is not quite correct.
They ARE assignment compatible, but can indeed have different sets of overloads.
As in the following example:
home: >./ta
Different types
home: >cat ta.pp
Type
TA = Integer;
TB = Type TA;
Var
A : TA;
B : TB;
begin
B:=1;
A:=B;
if TypeInfo(TA)<>TypeInfo(TB) then
Writeln('Different types');
end.
Michael.
_______________________________________________
fpc-pascal maillist - fpc-pascal@lists.freepascal.org
http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
