Am 31.10.2013 02:45, schrieb Xiangrong Fang:
2013/10/30 Jonas Maebe <jonas.ma...@elis.ugent.be
<mailto:jonas.ma...@elis.ugent.be>>
This is not equivalent. A private type declaration in a class adds
a new identifier that is visible inside that class. You then use
it, still in that class, to declare the return type of a function.
Next, in a scope where that type identifier is no longer visible,
you call the function.
My example is a complete match to that scenario as far as
identifier visibility is concerned (you use a type in a scope
where it is visible to declare a function return type, and then
call the function in a scope where it is not visible). In your
example, the type is not visible in the place where the function
is declared but only where it is defined
.
This is logically WRONG. Because to the machine, any function return
value can be seen as an array of bytes, for example, a pointer is
array[0..3] of Byte on a 32-bit machine. The purpose of type system
is to explain what these bytes stands for. So, if a type is
out-of-scope, how do you interpret the data?
The current "delphi compatible" implementation IS using the type
information to compile the program, i.e. although it is not visible,
it is indeed used by the compile, which, in my opinion, violates
visibility rules.
Standing on your view point, if a type is no longer visible, but a
variable (function return value) of that type is in current scope, and
understood by the program, this means, this value itself carries type
information! Is is kind of meta data available in Pascal? If so, I
think RTTI should work for ANY kind of primitive data types.
For unit interfaces there is indeed the point that if unit A uses unit B
then the program which uses unit A will be able to access types used by
unit A. E.g.:
=== unit A ===
unit A;
interface
type
TTest = class
procedure Test;
end;
implementation
procedure TTest.Test;
begin
Writeln('Foobar');
end;
end.
=== unit A ===
=== unit B ===
unit B;
interface
uses
A;
function SomeTest: TTest;
implementation
function SomeTest: TTest;
begin
Result := TTest.Create;
end;
end.
=== unit B ===
=== program ===
program test;
uses
B;
begin
// there won't be an error here
SomeTest.Test;
end.
=== program ===
It's this way at least since Turbo Pascal (though without classes then ;) ).
Regards,
Sven
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