Tomas Hajny wrote:
On Mon, November 18, 2013 07:38, Xiangrong Fang wrote:
Hi,
Is it possible to optionally use a unit? e.g.
unit myunit;
uses {$ifexists persist.pas}persist,{$endif} Classes;
type
TMyClass = class
public
{$ifexists persist.pas}
procedure SaveToStream(s: TStream);
{$endif}
end;
Isn't {$IFDEF PERSIST}... combined with calling the compiler with/without
-dPERSIST depending on availability of the source sufficient (and more
general)? Obviously, you can test availability of the source file in a
makefile/shell script/batch file/... and have the -dPERSIST added to
compiler options accordingly.
BTW, your example (and partly the whole concept) might give
unexpected/unwanted results - what if a precompiled version (.ppu/.o) of
that unit is available but not the source file? Which directories should
be checked when searching the file (note that the compiler couldn't know
if the filename mentioned should belong to a unit source file, specific
include file, compiled object, library or even a completely independent
file, and that different search paths are used for searching files of
different types)?
There are definitely hazards, but I think that an exists() predicate of
some form would definitely be useful. For example, inside an {$ifdef
persist} it would give the developers the ability to have a tailored
error message advising the maintainer that if persists.pas didn't exist
he should also get such-and-such a project from local svn, and set up
appropriate symlinks.
The major issue would be directories and search paths.
--
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk
[Opinions above are the author's, not those of his employers or colleagues]
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