Setting properties

[cstjean]

I'm interested in something like

@set object.property.x = 10

Can I support it? I get an error from assert_hasfields because, of course, property is not a field of object. I'd like to be able to implement setproperty(::Object, value, sym), similar to Base.setindex, which would return a new object with that property modified. Is that possible?

[jw3126]

Yes! You need to overload Setfield.setproperties(obj, patch::NamedTuple). In the next few days/weeks this is moved to the tiny dependency ConstructionBase, see also JuliaObjects/ConstructionBase.jl#1
So in future you only need to depend on ConstructionBase and overload ConstructionBase.setproperties(obj, patch::NamedTuple)

[jw3126]

See for an example here:

Setfield.jl/test/test_core.jl

Line 398 in 51bf096

struct CustomProperties

[cstjean]

It seems to work great, thank you!

[cstjean]

BTW, I haven't followed the entire discussion around constructor_of, but wouldn't it make sense to rewrite Setfield.jl around setproperties, with a fall-back to the constructor when it's not implemented? Relying on the constructor never felt quite right to me.

[jw3126]

I would say that Setfield.jl is already designed around setproperties. The default implementation just uses constructor_of. Try

Setfield.setproperties(MyType, patch) = ...
Setfield.constructor_of(::Type{<:MyType}) = error()

And Setfield.jl should work fine with MyType.