Re: How do you test whether a variable is static or not?
On Saturday, 30 July 2016 at 13:04:56 UTC, Ali Çehreli wrote:
On 07/30/2016 05:47 AM, Jonathan M Davis via
Digitalmars-d-learn wrote:
> I'm writing some serialization code where I need to skip
static variables.
> So, I have a symbol from a struct, and I'd like to test
whether it's static
> or not.
static variables don't have the .offsetof property:
struct S {
int a;
static int b;
}
// Bonus question: should field be alias or string?
template isStaticVar(T, alias field)
{
enum isStaticVar = !__traits(compiles, mixin("T." ~ field ~
".offsetof"));
}
void main() {
static assert (!isStaticVar!(S, "a"));
static assert (isStaticVar!(S, "b"));
}
Ali
This doesn't work, treats fields in base classes as static.
One way to test if a member is static is if it it doesn't exist
in tupleof... but this only returns the immediate members and so
will fail. I guess one will have to check all base types too and
if it doesn't exist in any of then it should be static.
Why is it so hard to be able to get basic information like if a
type is static or not?
Re: How do you test whether a variable is static or not?
On Saturday, 16 June 2018 at 08:52:20 UTC, DigitalDesigns wrote:
On Saturday, 30 July 2016 at 13:04:56 UTC, Ali Çehreli wrote:
On 07/30/2016 05:47 AM, Jonathan M Davis via
Digitalmars-d-learn wrote:
> I'm writing some serialization code where I need to skip
static variables.
> So, I have a symbol from a struct, and I'd like to test
whether it's static
> or not.
static variables don't have the .offsetof property:
struct S {
int a;
static int b;
}
// Bonus question: should field be alias or string?
template isStaticVar(T, alias field)
{
enum isStaticVar = !__traits(compiles, mixin("T." ~ field
~ ".offsetof"));
}
void main() {
static assert (!isStaticVar!(S, "a"));
static assert (isStaticVar!(S, "b"));
}
Ali
This doesn't work, treats fields in base classes as static.
One way to test if a member is static is if it it doesn't exist
in tupleof... but this only returns the immediate members and
so will fail. I guess one will have to check all base types
too and if it doesn't exist in any of then it should be static.
Why is it so hard to be able to get basic information like if a
type is static or not?
Probably because the symbols don't carry the information. I'd
reckon a compiler addition to __traits() would probably solve
this. Something like getStaticMembers
Re: How do you test whether a variable is static or not?
On 7/30/16 8:47 AM, Jonathan M Davis via Digitalmars-d-learn wrote: I'm writing some serialization code where I need to skip static variables. So, I have a symbol from a struct, and I'd like to test whether it's static or not. Ideally, I'd be able to do something like is(field == static) std.traits.hasStaticMember ? https://dlang.org/phobos/std_traits.html#hasStaticMember -Steve
Re: How do you test whether a variable is static or not?
On Saturday, June 16, 2018 14:55:51 Steven Schveighoffer via Digitalmars-d- learn wrote: > On 7/30/16 8:47 AM, Jonathan M Davis via Digitalmars-d-learn wrote: > > I'm writing some serialization code where I need to skip static > > variables. So, I have a symbol from a struct, and I'd like to test > > whether it's static or not. Ideally, I'd be able to do something like > > > > is(field == static) > > std.traits.hasStaticMember ? > > https://dlang.org/phobos/std_traits.html#hasStaticMember Yeah. I wrote that, and it got added to Phobos. If you'll note, my post in this thread was from almost two years ago. - Jonathan M Davis
Re: How do you test whether a variable is static or not?
On Saturday, 16 June 2018 at 21:41:37 UTC, Jonathan M Davis wrote: On Saturday, June 16, 2018 14:55:51 Steven Schveighoffer via Digitalmars-d- learn wrote: On 7/30/16 8:47 AM, Jonathan M Davis via Digitalmars-d-learn wrote: > I'm writing some serialization code where I need to skip > static variables. So, I have a symbol from a struct, and I'd > like to test whether it's static or not. Ideally, I'd be > able to do something like > > is(field == static) std.traits.hasStaticMember ? https://dlang.org/phobos/std_traits.html#hasStaticMember Yeah. I wrote that, and it got added to Phobos. If you'll note, my post in this thread was from almost two years ago. Haha! I usually don’t get caught with these old threads! -Steve
Re: How do you test whether a variable is static or not?
On Saturday, June 16, 2018 22:11:09 Steven Schveighoffer via Digitalmars-d- learn wrote: > On Saturday, 16 June 2018 at 21:41:37 UTC, Jonathan M Davis wrote: > > On Saturday, June 16, 2018 14:55:51 Steven Schveighoffer via > > > > Digitalmars-d- learn wrote: > >> On 7/30/16 8:47 AM, Jonathan M Davis via Digitalmars-d-learn > >> > >> wrote: > >> > I'm writing some serialization code where I need to skip > >> > static variables. So, I have a symbol from a struct, and I'd > >> > like to test whether it's static or not. Ideally, I'd be > >> > able to do something like > >> > > >> > is(field == static) > >> > >> std.traits.hasStaticMember ? > >> > >> https://dlang.org/phobos/std_traits.html#hasStaticMember > > > > Yeah. I wrote that, and it got added to Phobos. If you'll note, > > my post in this thread was from almost two years ago. > > Haha! I usually don’t get caught with these old threads! It's _really_ obvious in my e-mail reader, since I have threading turned on, and it the threads are sorted by the date of the first post in the thread, so the thread is way up in the list such that I'm only likely to even notice that such a post has been made if I tell my client to filter out read e-mails so that I can find the e-mails that I haven't read yet which aren't at the bottom where all of the recent stuff is. Someone could have replied in an old thread and really want me to respond, and I could easily not notice the message for weeks if I'm not trying to get the unread count down to zero and notice that once I've caught up with all of the recent messages, the number is still greater than zero. I kind of wish that the forum software discouraged against necro-ing threads like this, since they're easy for many of us to miss, and once someone replies to them and brings them to the front of the list in the forum software, folks tends to reply as if the thread were recent without noticing how old it is. - Jonathan M Davis
Re: How do you test whether a variable is static or not?
On Saturday, 16 June 2018 at 21:41:37 UTC, Jonathan M Davis wrote: On Saturday, June 16, 2018 14:55:51 Steven Schveighoffer via Digitalmars-d- learn wrote: On 7/30/16 8:47 AM, Jonathan M Davis via Digitalmars-d-learn wrote: > I'm writing some serialization code where I need to skip > static variables. So, I have a symbol from a struct, and I'd > like to test whether it's static or not. Ideally, I'd be > able to do something like > > is(field == static) std.traits.hasStaticMember ? https://dlang.org/phobos/std_traits.html#hasStaticMember Yeah. I wrote that, and it got added to Phobos. If you'll note, my post in this thread was from almost two years ago. - Jonathan M Davis doesn't work: ..\..\src\phobos\std\traits.d(3823): Error: class `app.A` member `z` is not accessible. What is the point of introspection if one can't get information about a type due to it's protection level? For example, how is one suppose to serialize a class that has protected and private members, which are common, when using properties?
Re: How do you test whether a variable is static or not?
On Saturday, June 16, 2018 22:56:38 DigitalDesigns via Digitalmars-d-learn wrote: > On Saturday, 16 June 2018 at 21:41:37 UTC, Jonathan M Davis wrote: > > On Saturday, June 16, 2018 14:55:51 Steven Schveighoffer via > > > > Digitalmars-d- learn wrote: > >> On 7/30/16 8:47 AM, Jonathan M Davis via Digitalmars-d-learn > >> > >> wrote: > >> > I'm writing some serialization code where I need to skip > >> > static variables. So, I have a symbol from a struct, and I'd > >> > like to test whether it's static or not. Ideally, I'd be > >> > able to do something like > >> > > >> > is(field == static) > >> > >> std.traits.hasStaticMember ? > >> > >> https://dlang.org/phobos/std_traits.html#hasStaticMember > > > > Yeah. I wrote that, and it got added to Phobos. If you'll note, > > my post in this thread was from almost two years ago. > > > > - Jonathan M Davis > > doesn't work: > > ..\..\src\phobos\std\traits.d(3823): Error: class `app.A` member > `z` is not accessible. > > What is the point of introspection if one can't get information > about a type due to it's protection level? > > For example, how is one suppose to serialize a class that has > protected and private members, which are common, when using > properties? The fact that you can't introspect on private variables with stuff like __traits is a well-known bug, and I expect that it will be fixed at some point. But if it's serialization that you want, then as I understand it, tupleof should work to get at the direct fields of a struct or class even if they're private. And you can always look at what a serialization library like Orange did. - Jonathan M Davis
Re: How do you test whether a variable is static or not?
On 6/16/18 6:23 PM, Jonathan M Davis wrote: I kind of wish that the forum software discouraged against necro-ing threads like this, since they're easy for many of us to miss, and once someone replies to them and brings them to the front of the list in the forum software, folks tends to reply as if the thread were recent without noticing how old it is. There is somewhat of a colorization of the date based on the age, but it's not drastic enough for ancient threads, and it's not as obvious as it would be if, say, the whole line was colored differently. -Steve
Re: How do you test whether a variable is static or not?
On 07/30/2016 05:47 AM, Jonathan M Davis via Digitalmars-d-learn wrote:
> I'm writing some serialization code where I need to skip static
variables.
> So, I have a symbol from a struct, and I'd like to test whether it's
static
> or not.
static variables don't have the .offsetof property:
struct S {
int a;
static int b;
}
// Bonus question: should field be alias or string?
template isStaticVar(T, alias field)
{
enum isStaticVar = !__traits(compiles, mixin("T." ~ field ~
".offsetof"));
}
void main() {
static assert (!isStaticVar!(S, "a"));
static assert (isStaticVar!(S, "b"));
}
Ali
Re: How do you test whether a variable is static or not?
On Saturday, 30 July 2016 at 12:47:10 UTC, Jonathan M Davis wrote:
I'm writing some serialization code where I need to skip static
variables. So, I have a symbol from a struct, and I'd like to
test whether it's static or not. Ideally, I'd be able to do
something like
is(field == static)
but of course that doesn't work. There is
__traits(isStaticFunction, ...),
but there is no __traits(isStaticVariable, ...) or
__traits(isStatic, ...),
and I don't see anything in std.traits which would help. The
closest that
I've been able to come up with is
template isStaticVar(T, alias field)
{
enum isStaticVar =
is(typeof({mixin("auto i = T." ~ field.stringof ~
";");}));
}
For a more general solution, it would of course need to verify
that the field wasn't a function as well, but in my case, that
was already checked prior to instantiating isStaticVar, so I
can skip it here. And what I have mostly works. However, it
would fail miserably if the field were a static member variable
that was non-copyable. If it were, then that code would would
declare it to be non-static. Now, non-copyable structs are rare
enough that I can probably get away with letting that bug
stand, but I'd prefer to correctly detect whether a variable is
static or not. Does anyone have a better idea of how to do this?
- Jonathan M Davis
You won't be able to assign it if it's not static. Given this
isStaticVar(Stuff) = __traits(compiles, Stuff =
typeof(Stuff).init))
Unfortuantely it's hard to make a stand alone template for this.
For example I was not able to verify the non-static case
struct Foo
{
static int a;
int b;
}
template isStaticVar(alias stuff)
{
bool check()
{
bool result;
static if (!is(typeof(__traits(parent, stuff
result = true;
else static if (__traits(compiles, stuff =
typeof(stuff).init))
result = true;
return result;
}
enum isStaticVar = check();
}
unittest
{
static assert(isStaticVar!(Foo.a));
//static assert(isStaticVar!(Foo.b));
}
I'm curious to see the other solutions.
Re: How do you test whether a variable is static or not?
On Saturday, 30 July 2016 at 13:04:56 UTC, Ali Çehreli wrote:
On 07/30/2016 05:47 AM, Jonathan M Davis via
Digitalmars-d-learn wrote:
> I'm writing some serialization code where I need to skip
static variables.
> So, I have a symbol from a struct, and I'd like to test
whether it's static
> or not.
static variables don't have the .offsetof property:
struct S {
int a;
static int b;
}
// Bonus question: should field be alias or string?
template isStaticVar(T, alias field)
{
enum isStaticVar = !__traits(compiles, mixin("T." ~ field ~
".offsetof"));
}
void main() {
static assert (!isStaticVar!(S, "a"));
static assert (isStaticVar!(S, "b"));
}
Ali
Wow, this is directly for std.traits !
Re: How do you test whether a variable is static or not?
On Saturday, July 30, 2016 06:04:56 Ali Çehreli via Digitalmars-d-learn wrote:
> On 07/30/2016 05:47 AM, Jonathan M Davis via Digitalmars-d-learn wrote:
> > I'm writing some serialization code where I need to skip static
>
> variables.
>
> > So, I have a symbol from a struct, and I'd like to test whether it's
>
> static
>
> > or not.
>
> static variables don't have the .offsetof property:
>
> struct S {
> int a;
> static int b;
>
> // Bonus question: should field be alias or string?
That depends on what you're doing. __traits(allMembers, ...) gives you a
list of strings, so it may make more sense in the general case to use
string, but in order to actually do much of anything useful, you have to
convert them all to symbols, which is what I've done in my code and why I
was using an alias.
> template isStaticVar(T, alias field)
> {
> enum isStaticVar = !__traits(compiles, mixin("T." ~ field ~
> ".offsetof"));
> }
>
> void main() {
> static assert (!isStaticVar!(S, "a"));
> static assert (isStaticVar!(S, "b"));
> }
Thanks!
- Jonathan M Davis
