Vinzent Höfler schrieb:
On Wed, 02 Nov 2011 07:35:30 +0100, Felipe Monteiro de Carvalho
<felipemonteiro.carva...@gmail.com> wrote:
Maybe that would be something interresting to add. Programs that want
to measure time differences could use it instead of hacking Now.
Well, all what's needed is to differentiate between a political-time
and a monotonic/real-time clock.
The latter could be sufficiently substituted on all systems by the
underlying facilities of the system with opaque time types. The RTL
could provide all necessary conversion functions, so not even the
actual resolution of the system would matter.
IMO we have to face a problem very similar to Ansi/UTF-8/16: A TDateTime
variable can contain local time in a number of timezones (Ansi), or UTC
values (UTF), which must be interpreted accordingly, e.g. in
DateTimeToStr().
When Delphi compatible Now() provides local time TDateTime (including
DST, as is on Windows), and DateTimeToStr() etc. expect a local time
argument, a full emulation of these functions has to be provided on
other platforms as well.
But Delphi also offers a (monotonic) modified Julian date (type Double),
and TTimeStamp, and conversions are required when such values shall be
formatted into strings. With overloaded functions the monotonic/local
time conversion can be performed in the formatting etc. functions, and
specialized functions to get the time in other encodings can be added.
Another feature could switch the application-wide TDateTime content,
between local (Windows default) and monotonic/UTC (POSIX) time. This
would not require additional functions, instead all date/time functions
would take into account that setting internally. Drawback is that only
one encoding can be used in an application, i.e. the user must decide
whether times are used as unique (monotonic, real-time) time stamps, or
in local time for display purposes.
As a third solution the time encoding could be added to TDateTime,
similar to the new AnsiString encoding. Care must be taken to keep such
an extension compatible with e.g. typecasts (Double from/to TDateTime).
Perhaps a conversion of TDateTime into an Object with an added Encoding
property would help...
DoDi
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