Re: Deriving a struct from another one via template: Easy way to propagate UDAs?
On Saturday, 16 March 2024 at 20:34:57 UTC, Inkrementator wrote: Nice. Btw I vaguely remember you also wrote about how and why to reduce the usage string mixins, with some real example of alternative techniques you used go to the main page: http://dpldocs.info/this-week-in-d/Blog.html and use ctrl+f and hope i said it in the summary lol but the two that pop up there are: http://dpldocs.info/this-week-in-d/Blog.Posted_2022_12_26.html#more-mixin-techniques and https://forum.dlang.org/post/fbcltjuysmjrxmebe...@forum.dlang.org The general rule is to try to use the local name inside the string instead of concatenating its result, and remember the built in compiler-tuple - which is what __traits(getAttributes) and the parameters reflection and other things - can be used directly in a lot of places, you can very often substitute one of those for a value and it will put it in for you. I encourage you to experiment with plugging these things directly in at the use site and seeing what happens before falling back to strings. fyi don't really follow this forum anymore, you got a bit lucky that i popped in for the dconf online link, so i might not see any further replies to this.
Re: Deriving a struct from another one via template: Easy way to propagate UDAs?
On Saturday, 16 March 2024 at 13:09:13 UTC, Adam D Ruppe wrote:
On Thursday, 14 March 2024 at 23:19:37 UTC, Inkrementator wrote:
@(__traits(getAttributes, thingYouWantToForward))
void yourNewThing() {}
Thanks, that should solve my problem.
http://dpldocs.info/this-week-in-d/Blog.Posted_2020_01_20.html#understanding-mixin-templates
Nice. Btw I vaguely remember you also wrote about how and why to
reduce the usage string mixins, with some real example of
alternative techniques you used, but I can't find it anymore. The
search query 'site:dpldocs.info string mixin "This week in D"' as
well as "site:arsdnet.net mixin" don't produce it. Can you link
it to me?
Re: Deriving a struct from another one via template: Easy way to propagate UDAs?
On Friday, 15 March 2024 at 19:13:38 UTC, cc wrote:
This is trivially easy if your types are visible at module
level, and mixin is a fine tool for the job. It doesn't work
quite so well with [Voldemort
types](https://wiki.dlang.org/Voldemort_types).
I used the following lines to make it work for Unknown and I
think even Voldemort types.
```d
static foreach(att; allFieldTypes){
//pragma(msg, "alias %s =att;\n".format(att.stringof));
mixin("alias %s = att;\n".format(att.stringof));
}
```
But I don't know how to do this (in a general) for UDAs, since
they can be values instead of types too, i.e. @UDA(Voldemort!2(3))
Re: Deriving a struct from another one via template: Easy way to propagate UDAs?
On Thursday, 14 March 2024 at 23:19:37 UTC, Inkrementator wrote:
* Is UDA propagation possible without string mixins?
@(__traits(getAttributes, thingYouWantToForward))
void yourNewThing() {}
* Are template mixins vulnerable to name collisions?
http://dpldocs.info/this-week-in-d/Blog.Posted_2020_01_20.html#understanding-mixin-templates
Re: Deriving a struct from another one via template: Easy way to propagate UDAs?
On Thursday, 14 March 2024 at 23:19:37 UTC, Inkrementator wrote:
I am trying to derive a struct from another. I want to modify
each field such that type of it goes from some T to Nullable!T,
preserving all fieldnames and UDAs.
This is trivially easy if your types are visible at module level,
and mixin is a fine tool for the job. It doesn't work quite so
well with [Voldemort
types](https://wiki.dlang.org/Voldemort_types).
```d
struct MyUDA { int q; }
struct Foo { int f; }
struct MyStruct {
@MyUDA(3) int x;
@MyUDA(4) Foo f;
@MyUDA(5) @MyUDA(7) string s;
}
auto generateUDAs(A...)() {
string[] udaStrs;
static foreach (uda; A)
udaStrs ~= "@(" ~ uda.stringof ~ ")";
return udaStrs;
}
struct Wrapped(S) {
static foreach (idx, field; S.tupleof) {
//pragma(msg, format(... can be used to preview
mixin(format("%s %s %s;", generateUDAs!(__traits(getAttributes,
field)).join(' '), Nullable!(typeof(field)).stringof,
field.stringof));
}
}
void main() {
MyStruct s;
s.x = 3;
s.f = Foo(1);
s.s = null;
Wrapped!MyStruct w;
w.x = s.x;
w.f = s.f;
w.s = s.s;
w.x.nullify;
w.f.nullify;
w.s.nullify; // strings/objects are already nullable though
static assert(__traits(getAttributes, w.s) ==
AliasSeq!(MyUDA(5), MyUDA(7)));
}
```
If you absolutely must though, you could do something like
```d
enum WrapMixin = q{
struct Wrapped(S) {
static foreach (field; S.tupleof)
mixin(format("%s %s %s;",
generateUDAs!(__traits(getAttributes, field)).join(' '),
Nullable!(typeof(field)).stringof, field.stringof));
}
};
void main() {
struct MyUDA { .
struct MyStruct { .
mixin(WrapMixin);
Wrapped!MyStruct w;
}
```
