Re: Can attributes trigger functionality?
On Wednesday, 6 September 2017 at 02:43:20 UTC, Psychological Cleanup wrote: I'm having to create a lot of boiler plate code that creates "events" and corresponding properties(getter and setter). I'm curious if I can simplify this without a string mixin. If I create my own attribute like @Event double foo(); and I write any code that will trigger when the event is used and add more code(such as the setter property and events that I need? Obviously I could write some master template that scans everything, but that seems to be far too much over kill. A string mixin is probably my only option but is a bit ulgy for me. Since attributes can be defined by structures it seems natural that we could put functionality in them that are triggered when used but I'm unsure if D has such capabilities. Thanks. User defined attributes (UDAs) are in and of themselves only (compile time) introspectable decoration [1] (they only carry information). If you want to trigger specific behaviour for things that are attributed with a UDA you indeed need to some custom written active component that introspects using `__traits(getAttributes, symbol) and generates injects generates the behaviour (e.g. using a string mixin as you noted). [1] https://dlang.org/spec/attribute.html#UserDefinedAttribute
Re: Can attributes trigger functionality?
On Wednesday, 6 September 2017 at 02:43:20 UTC, Psychological
Cleanup wrote:
I'm having to create a lot of boiler plate code that creates
"events" and corresponding properties(getter and setter).
I'm curious if I can simplify this without a string mixin.
You certainly don't need a string mixin, but you do need some
code to react to the attribute.
Here's one that generates a wrapper function on-demand:
---
import std.stdio;
import std.traits;
class Test {
@cool void foo_() {
writeln("cool function called");
}
mixin CoolFunctions;
}
// our UDA
enum cool;
// adds the decorator implementation
mixin template CoolFunctions() {
template opDispatch(string name)
if(hasUDA!(__traits(getMember, typeof(this), name ~ "_"), cool)) {
auto opDispatch(Parameters!(__traits(getMember,
typeof(this), name ~ "_")) params) {
writeln("cool before");
scope(success) {
writeln("cool after");
}
return __traits(getMember, this, name ~
"_")(params);
}
}
}
void main() {
auto test = new Test();
test.foo();
}
-
No string mixin (uses a mixin template instead), and not even a
loop over the functions - it does them on-demand when used via
opDispatch.
Can attributes trigger functionality?
I'm having to create a lot of boiler plate code that creates "events" and corresponding properties(getter and setter). I'm curious if I can simplify this without a string mixin. If I create my own attribute like @Event double foo(); and I write any code that will trigger when the event is used and add more code(such as the setter property and events that I need? Obviously I could write some master template that scans everything, but that seems to be far too much over kill. A string mixin is probably my only option but is a bit ulgy for me. Since attributes can be defined by structures it seems natural that we could put functionality in them that are triggered when used but I'm unsure if D has such capabilities. Thanks.
