SysTime in a Struct

[Jonathan M Davis]

On Thursday, March 01, 2012 16:00:09 Ali Çehreli wrote:
> On 03/01/2012 03:46 PM, albatroz wrote:
> > Hi Ali, just tring to define a type that holds this information. It was
> > just an attempt to create a type DateTime with the values from the known
> > strings, I thought it was possible to create the definition directly in
> > the Struct, with no need for an external function.
> > edate and etime are strings that I will read in to the struct, but for
> > operations with time and dates I need to create/define a DateTime type.
> 
> From that description, it looks like you can hold edate etc. as members
> and produce SysTime as needed. The following demonstrates how to convert
> preEv to SysTime by opCast implicitly and by sys_time explicitly:
> 
> import std.stdio;
> import std.conv;
> import std.datetime;
> 
> struct preEv
> {
> string edate; //010112
> string etime; //00:00:00
> string etext; //
> 
> SysTime opCast(T : SysTime)() const
> {
> return SysTime(DateTime(
> Clock.currTime.year,
> to!int(this.edate[2..4]),
> to!int(this.edate[0..2]),
> to!int(etime[0..2]),
> to!int(etime[3..5]),
> to!int(etime[6..8])));
> }
> 
> SysTime sys_time() const @property
> {
> return to!SysTime(this);
> }
> }
> 
> void main()
> {
> auto pe = preEv("010312", "15:53:00", "The event");
> 
> // Explicit conversion
> auto st0 = to!SysTime(pe);
> writeln(st0);
> 
> // Casting
> auto st1 = cast(SysTime)(pe);
> writeln(st1);
> 
> // As a property
> auto st2 = pe.sys_time;
> writeln(st2);
> }
> 
> If you think that you need to cache SysTime in the object itself, you
> can do that for example in opCast.
> 
> On the other hand, if all you need to store is SysTime and etext, then
> you need to create SysTime in the constructor:
> 
> import std.stdio;
> import std.conv;
> import std.datetime;
> 
> struct preEv
> {
> SysTime time;
> string etext;
> 
> this (string edate, string etime, string etext)
> {
> this.time = SysTime(DateTime(
> Clock.currTime.year,
> to!int(edate[2..4]),
> to!int(edate[0..2]),
> to!int(etime[0..2]),
> to!int(etime[3..5]),
> to!int(etime[6..8])));
> this.etext = etext;
> }
> }
> 
> void main()
> {
> auto pe = preEv("010312", "15:53:00", "The event");
> 
> writeln(pe.time);
> }


You know, you can create a TimeOfDay from "15:53:00" with 
TimeOfDay.fromISOExtString. That won't work with the date, since it's not in 
either the ISO or ISO Extended format, but it would work for the time.

I'd also point out that currTime isn't a property (since it takes an optional 
TimeZone argument), so you really should be using parens when you call it. 
Otherwise, once property enforcement is enabled, your code won't compile.

Also, you should use std.conv.to, not a cast, when converting, since 
std.conv.to now supports calling user-defined opCasts, and there's less risk of 
screwing up the cast if you use std.conv.to. So, defining an opCast is fine, but 
it should probably be used with std.conv.to rather than directly.

- Jonathan M Davis