• Laeeth Isharc (14/14) Sep 13 2015 can I check if a member of a T has a member without using a mixin?
• wobbles (2/17) Sep 13 2015 Use __traits(compiles, date.second)?
• Laeeth Isharc (8/9) Sep 13 2015 Thanks.
• BBasile (4/13) Sep 13 2015 can't you use 'hasMember' (either with __traits() or
• Laeeth Isharc (10/28) Sep 14 2015 I'll check again in a bit, but I seem to recall hasMember didn't
• John Colvin (2/15) Sep 14 2015 You mean hasMember!(typeof(T.bar.date), "hour"), right?
• Laeeth Isharc (4/21) Sep 14 2015 Ahh. Probably that was why (I will check it shortly). Why do I
• John Colvin (8/30) Sep 14 2015 T.bar.date is just a symbol. If you tried to actually access it

Laeeth Isharc <spamnolaeeth nospamlaeeth.com> writes:

can I check if a member of a T has a member without using a mixin?

hid_t createDataType(T)()
if (__traits(isSame, TemplateOf!(T), PriceBar))
{
	auto tid=H5T.create(H5TClass.Compound,T.sizeof);
	enum offsetof(alias type, string field) = mixin(type.stringof 
~"."~field~".offsetof");
	H5T.insert(tid, "date", offsetof!(T,"date"), 
createDataType!(KalDate));
	static if(hasMember!(T,"open"))
		H5T.insert(tid,"open",offsetof!(T,"open"),mapDtoHDF5Type("double"));
}

I would like to check if date has a member called second.

Thanks.

wobbles <grogan.colin gmail.com> writes:

On Sunday, 13 September 2015 at 16:46:54 UTC, Laeeth Isharc wrote:
 can I check if a member of a T has a member without using a 
 mixin?

 hid_t createDataType(T)()
 if (__traits(isSame, TemplateOf!(T), PriceBar))
 {
 	auto tid=H5T.create(H5TClass.Compound,T.sizeof);
 	enum offsetof(alias type, string field) = mixin(type.stringof 
 ~"."~field~".offsetof");
 	H5T.insert(tid, "date", offsetof!(T,"date"), 
 createDataType!(KalDate));
 	static if(hasMember!(T,"open"))
 		H5T.insert(tid,"open",offsetof!(T,"open"),mapDtoHDF5Type("double"));
 }

 I would like to check if date has a member called second.

 Thanks.

Use __traits(compiles, date.second)?

Laeeth Isharc <spamnolaeeth nospamlaeeth.com> writes:

On Sunday, 13 September 2015 at 17:09:57 UTC, wobbles wrote:
 Use __traits(compiles, date.second)?


Thanks.

This works:

static if (__traits(compiles, { T bar; bar.date.hour;}))
		pragma(msg,"hour");
	else
		pragma(msg,"nohour");
	

BBasile <bb.temp gmx.com> writes:

On Sunday, 13 September 2015 at 17:24:20 UTC, Laeeth Isharc wrote:
 On Sunday, 13 September 2015 at 17:09:57 UTC, wobbles wrote:
 Use __traits(compiles, date.second)?


 Thanks.

 This works:

 static if (__traits(compiles, { T bar; bar.date.hour;}))
 		pragma(msg,"hour");
 	else
 		pragma(msg,"nohour");
 	

can't you use 'hasMember' (either with __traits() or 
std.traits.hasMember)? It's more idiomatic than checking if it's 
compilable.

Laeeth Isharc <spamnolaeeth nospamlaeeth.com> writes:

On Sunday, 13 September 2015 at 17:34:11 UTC, BBasile wrote:
 On Sunday, 13 September 2015 at 17:24:20 UTC, Laeeth Isharc 
 wrote:
 On Sunday, 13 September 2015 at 17:09:57 UTC, wobbles wrote:
 Use __traits(compiles, date.second)?


 Thanks.

 This works:

 static if (__traits(compiles, { T bar; bar.date.hour;}))
 		pragma(msg,"hour");
 	else
 		pragma(msg,"nohour");
 	

 can't you use 'hasMember' (either with __traits() or 
 std.traits.hasMember)? It's more idiomatic than checking if 
 it's compilable.

I'll check again in a bit, but I seem to recall hasMember didn't 
work.  I would like to get the type of a member of a type, and I 
think hasMember!(T.bar.date","hour") didn't work for that.  
Possibly it does work and I messed it up somehow, or it doesn't 
work and there is a more elegant way.

Someone ought to write a tutorial showing how to use the good 
stuff we have to solve real problems.  Eg an annotated babysteps 
version of Andrei's allocator talk.  I can't do it as too much on 
my plate.

John Colvin <john.loughran.colvin gmail.com> writes:

On Monday, 14 September 2015 at 14:05:01 UTC, Laeeth Isharc wrote:
 On Sunday, 13 September 2015 at 17:34:11 UTC, BBasile wrote:
 On Sunday, 13 September 2015 at 17:24:20 UTC, Laeeth Isharc 
 wrote:
 [...]

 can't you use 'hasMember' (either with __traits() or 
 std.traits.hasMember)? It's more idiomatic than checking if 
 it's compilable.

 I'll check again in a bit, but I seem to recall hasMember 
 didn't work.  I would like to get the type of a member of a 
 type, and I think hasMember!(T.bar.date","hour") didn't work 
 for that.  Possibly it does work and I messed it up somehow, or 
 it doesn't work and there is a more elegant way.

You mean hasMember!(typeof(T.bar.date), "hour"), right?

Laeeth Isharc <spamnolaeeth nospamlaeeth.com> writes:

On Monday, 14 September 2015 at 14:21:12 UTC, John Colvin wrote:
 On Monday, 14 September 2015 at 14:05:01 UTC, Laeeth Isharc 
 wrote:
 On Sunday, 13 September 2015 at 17:34:11 UTC, BBasile wrote:
 On Sunday, 13 September 2015 at 17:24:20 UTC, Laeeth Isharc 
 wrote:
 [...]

 can't you use 'hasMember' (either with __traits() or 
 std.traits.hasMember)? It's more idiomatic than checking if 
 it's compilable.

 I'll check again in a bit, but I seem to recall hasMember 
 didn't work.  I would like to get the type of a member of a 
 type, and I think hasMember!(T.bar.date","hour") didn't work 
 for that.  Possibly it does work and I messed it up somehow, 
 or it doesn't work and there is a more elegant way.

 You mean hasMember!(typeof(T.bar.date), "hour"), right?

Ahh.  Probably that was why (I will check it shortly).  Why do I 
need to do a typeof?  What kind of thing is T.bar.date before the 
typeof given that T is a type?

John Colvin <john.loughran.colvin gmail.com> writes:

On Monday, 14 September 2015 at 15:04:00 UTC, Laeeth Isharc wrote:
 On Monday, 14 September 2015 at 14:21:12 UTC, John Colvin wrote:
 On Monday, 14 September 2015 at 14:05:01 UTC, Laeeth Isharc 
 wrote:
 On Sunday, 13 September 2015 at 17:34:11 UTC, BBasile wrote:
 On Sunday, 13 September 2015 at 17:24:20 UTC, Laeeth Isharc 
 wrote:
 [...]

 can't you use 'hasMember' (either with __traits() or 
 std.traits.hasMember)? It's more idiomatic than checking if 
 it's compilable.

 I'll check again in a bit, but I seem to recall hasMember 
 didn't work.  I would like to get the type of a member of a 
 type, and I think hasMember!(T.bar.date","hour") didn't work 
 for that.  Possibly it does work and I messed it up somehow, 
 or it doesn't work and there is a more elegant way.

 You mean hasMember!(typeof(T.bar.date), "hour"), right?

 Ahh.  Probably that was why (I will check it shortly).  Why do 
 I need to do a typeof?  What kind of thing is T.bar.date before 
 the typeof given that T is a type?

T.bar.date is just a symbol. If you tried to actually access it 
then it would have to be a compile-time construct or be a static 
member/method, but it's perfectly OK to ask what type it has or 
what size it has.

The simple story: hasMember takes a type as its first argument. 
T.bar.date isn't a type, it's a member of a member of a type. To 
find out what type it is, use typeof.