On Tuesday, 2 June 2015 20:02:00 UTC+1, [email protected] wrote:
>
> Simon,
>
> I have deleted my old implementation of modifyField! and have now switched
> over to your implementation, which is really nice. Please view the latest
> commit:
>
> https://github.com/StephenVavasis/Modifyfield.jl
>
>
Looks good!
> It is not quite working yet, and perhaps you can help. The issue is that
> the macros @modify_field! and @modify_tuple_entry! are not being exported
> by the package even though they are declared for export. Here is the error
> message.
>
> julia> include(Pkg.dir("Modifyfield") * "/test_modifyfield.jl")
> ERROR: LoadError: UndefVarError: @modify_field! not defined
> in include at boot.jl:252
> in include_from_node1 at loading.jl:133
> while loading
> c:\Users\vavasis\Documents\.julia\v0.4\Modifyfield\test_modifyfiel
> d.jl, in expression starting on line 11
>
> Oddly, the exporting works fine when I load the package manually (i.e.,
> include("c:/.../Modifyfield.jl")) instead of automatically (i.e.,
> Pkg.clone("https://github.com/StephenVavasis./Modifyfield.jl";)) . I have
> never written a package with macros before, so perhaps I am making some
> foolish mistake?
>
If you move the file Modifyfield.jl into /src subdirectory, it should work
when you type "using Modifyfield"
>
> Beyond this, I have a few comments/questions:
>
> (1) Although I didn't use it, regarding your suggestion of "eltype" to
> determine the base type of an array: Unfortunately, this does not work in
> general because eltype in general returns the type that comes out of a
> start/done/next loop rather than a getindex call. For example,
> eltype(Dict{K,V}()) == (K,V)
>
True, but the implementation of eltype is fairly simple, so you could write
a function that does what you need.
> (2) I did not understand the use of symbol in :call, symbol(x) in the code
> that you provided. In fact, :call, x works fine because in Julia you can
> call a type to get the constructor. Am I missing something?
>
No, you're right: when I was writing this I couldn't get it to work, but
the problem must have been elsewhere.
> (3) I also did not understand why you put esc around argument x but not v
> in your code snippet. Based on my (possibly incorrect) understanding of
> esc, it seems like both x and v should be escaped, which is what I have
> implemented. Perhaps you can clarify this.
>
Honestly, I still don't quite understand the escaping rules: what I usually
do is write something that seems close, then call macroexpand on a quoted
macro call, e.g.
macroexpand(:(@modify_field! y.isadded = false))
> (4) Finally, building upon your ingenious code, I also added a
> @modify_tuple_entry! macro to the package. I'd appreciate your comments on
> that as well.
>
>
> On Tuesday, June 2, 2015 at 8:16:29 AM UTC-4, Simon Byrne wrote:
>>
>> On 2 June 2015 at 13:00, David Gold <[email protected]> wrote:
>> > @Simon: why safer? Rather, what is unsafe about calling symbol within
>> the Expr constructor?
>>
>> I wasn't quite sure how the scoping worked (i.e. what would happen if
>> the type had not been exported?), but it does seem to be safe.
>>
>
