Jack Stouffer and I have been working on a pull request for
Phobos to enable runtime dispatch for field and property access:
https://github.com/D-Programming-Language/phobos/pull/4070
(It's useful when directly porting code from dynamic languages
like Python.)
Working with fields in this fashion is pretty easy, but I've hit
a snag for property methods: if even one of the available
property methods is impure, unsafe, etc., then the dispatch
function must also be impure/unsafe/whatever.
In order for the dispatch function to be usable in
pure/@safe/etc. code, it needs to filter out those property
methods which are not. This is simple enough - except that
*which* attributes are required cannot be inferred from the
context; it must be explicitly specified by the user of the
dispatch template - somehow...
A naive way to do it would be this:
template example(string attrs = "pure @safe nothrow @nogc")
{
mixin("void example() " ~ attrs ~ " { /* do something */
}");
}
Which could then be used like this:
example!"pure @safe @SomeUDA"();
That's pretty ugly though, since it requires that all template
functions with explicit attribute control be implemented as
string mixins.
Is there a better way to do this? If not, I think consideration
should be given (long-term) to adding an "attribute set"
construct as a new type of template parameter.
