# Dynamically documenting fields in "dictionary-like" type

**URL:** <https://discourse.julialang.org/t/dynamically-documenting-fields-in-dictionary-like-type/25295>\
**Category:** General Usage\
**Created:** [June 14, 2019, 9:09am UTC](https://discourse.julialang.org/t/dynamically-documenting-fields-in-dictionary-like-type/25295 "2019-06-14T09:09:00Z")\
**Posts on this page:** 6\
**Page:** 1

<div class="post-metadata">

**Author:** ![sebasguts](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/sebasguts/32/8921_2.png) [@sebasguts](https://discourse.julialang.org/u/sebasguts)\
**Post date:** [June 14, 2019, 9:09am UTC](https://discourse.julialang.org/t/dynamically-documenting-fields-in-dictionary-like-type/25295/1 "2019-06-14T09:09:00Z")

</div>

Dear all,

I a trying to add dynamic documentation to fields of a “dictionary-like” type in GAP.jl, namely the type

```julia
struct GlobalsType
    funcs::Dict{Symbol,Cuint}
end

```

There is only one global instance of this type, namely `GAP.Globals`, and its `getproperty` function is overloaded to return objects of a single type, namely `MPtr`.

I am now trying to add dynamic documentation to those `MPtr` objects by adding

```julia
Docs.getdoc(x::MPtr) = GAP_help( gap_to_julia( String, Globals.NameFunction( x ) ) )

```

The function returns the right string. However, if I try to do

```julia
help?> GAP.Globals.SymmetricGroup

```

I get the following error

```julia
help?> GAP.Globals.SymmetricGroup
ERROR: MethodError: no method matching Base.Docs.Binding(::GAP.GlobalsType, ::Symbol)
Closest candidates are:
  Base.Docs.Binding(::Module, ::Symbol) at docs/bindings.jl:12

```

Theoretically, the function `getdoc` would return the right documentation string, if it is called on `GAP.Globals.SymmetricGroup`

However, I think the error is due to the fact that `Globals` is not a module. Since GAP changes its global names at runtime, I cannot make `Globals` a module, as I have to ask GAP if the object exist.

Is there a way to dynamically add documentations for such field entries?

Best, and thanks a lot,  
Sebastian

---

<div class="post-metadata">

**Author:** ![JeffreySarnoff](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jeffreysarnoff/32/1980_2.png) [@JeffreySarnoff](https://discourse.julialang.org/u/JeffreySarnoff)\
**Post date:** [June 14, 2019, 4:54pm UTC](https://discourse.julialang.org/t/dynamically-documenting-fields-in-dictionary-like-type/25295/2 "2019-06-14T16:54:07Z")

</div>

just to clarify  
The `struct` has no field `NameFunction`, yet you call `Globals.NameFunction` (which looks like it is `GAP.Globals.NameFunction` because the only instance of your `struct` is `GAP.Globals`). Is there a separate thing that is named `Globals` and is not `GAP.Globals`?

---

<div class="post-metadata">

**Author:** ![sebasguts](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/sebasguts/32/8921_2.png) [@sebasguts](https://discourse.julialang.org/u/sebasguts)\
**Post date:** [June 14, 2019, 6:02pm UTC](https://discourse.julialang.org/t/dynamically-documenting-fields-in-dictionary-like-type/25295/3 "2019-06-14T18:02:22Z")

</div>

Hi, thanks for your question and interest.

The `Globals` object automatically generates an object using its `getproperty` function. So while this entry does not exists a priory, it gets generated (i.e., an `MPtr` type object is returned). Does this help?

---

<div class="post-metadata">

**Author:** ![JeffreySarnoff](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jeffreysarnoff/32/1980_2.png) [@JeffreySarnoff](https://discourse.julialang.org/u/JeffreySarnoff)\
**Post date:** [June 14, 2019, 7:21pm UTC](https://discourse.julialang.org/t/dynamically-documenting-fields-in-dictionary-like-type/25295/4 "2019-06-14T19:21:26Z")

</div>

not yet 🙂

It would be helpful to have each step given its own tiny function. I am trying to see where the normative process with Doc needs to fit. You have collapsed too much for that purpose (to one who has no familiarity with your project).

Again, to clarify: (please correct as appropriate)  
Each GAP function is assigned a `Symbol`,something that takes the place of the actual function name (as a string)?

(a) is there a function that takes the string-form function name and returns the corresponding symbol?  
(b) like (a) except returns the corresponding MPtr?

c) What is the relationship of Cuint value and the function symbol and also the function MPtr?  
(d) what does NameFunction return?

---

<div class="post-metadata">

**Author:** ![sebasguts](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/sebasguts/32/8921_2.png) [@sebasguts](https://discourse.julialang.org/u/sebasguts)\
**Post date:** [June 17, 2019, 6:05am UTC](https://discourse.julialang.org/t/dynamically-documenting-fields-in-dictionary-like-type/25295/6 "2019-06-17T06:05:59Z")

</div>

Hi,  
I am sorry for the late reply, I was afk for the weekend.

> Each GAP function is assigned a `Symbol` ,something that takes the place of the actual function name (as a string)?

Yes, indeed. I am sorry for not having this clarified enough. The `getproperty` function of `GlobalsType` basically looks like this:

```julia
getproperty(x::GlobalsType,name::Symbol)
    get cuint assiciated to name from GAP
    store name and cuint in x
    get mptr from cuint
    return MPtr
end

```

It basically fetches a new MPtr all the time, associated to the global name `name` in GAP. The `Cuint` is only GAP’s internal representation of the global variable with name `name`. We store it so we do not have to resolve the name all the time (the map `cuint` → `MPtr` might change, but not `name` → `cuint`.

Hope this helps.

---

<div class="post-metadata">

**Author:** ![pfitzseb](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/pfitzseb/32/45566_2.png) [@pfitzseb](https://discourse.julialang.org/u/pfitzseb)\
**Post date:** [June 17, 2019, 8:48am UTC](https://discourse.julialang.org/t/dynamically-documenting-fields-in-dictionary-like-type/25295/7 "2019-06-17T08:48:27Z")

</div>

Pretty sure you can just define

```julia
Base.Docs.Binding(x::MPtr, s::Symbol) = getproperty(x, s)

```

and your code will just work:

```julia
julia> using Random

julia> struct Foo end

julia> Base.Docs.getdoc(o::Foo) = Text(randstring(10))

julia> Base.Docs.Binding(::Foo, ::Symbol) = nothing # or getproperty(...)

julia> x = Foo()
Foo()

help?> x
search: x xor exp Expr exp2 exit axes expm1 exp10 export extrema exponent Exception expanduser

eZSu6n8dME

help?> x
search: x xor exp Expr exp2 exit axes expm1 exp10 export extrema exponent Exception expanduser

C27YWQpr89

```