Proposition: Change meta (add get(nlp, :thing))

[abelsiqueira]

Instead of using nlp.meta.nvar, use get(nlp, :nvar) or getfield.

In particular, a related problem is in the NLS #91 nls_meta. Since we don't have OO, we can't have nls_meta extending meta only including nequ. With the proposed change, though, we can define

abstract AbstractNLSMeta
type NLSMeta <: AbstractNLSMeta
  meta :: AbstractNLPMeta
  nequ :: Int
end
abstract AbstractNLSModel
type LLSModel <: AbstractNLSModel
  meta :: NLSMeta
  A :: Matrix
  b :: Vector
end

meta(nlp :: AbstractNLPModel) = nlp.meta
meta(nls :: AbstractNLSModel) = nls.meta.meta
get(nlp :: AbstractNLPModel, name :: Symbol) = getfield(meta(nlp), name)

[dpo]

We could probably use an overarching AbstractMeta. Using metaprogramming, we can probably define methods

nvar(model::AbstractNLPModel) = model.meta.nvar
ncon(model::AbstractNLPModel) = model.meta.nvar
...

which may look more intuitive than get()!?

[abelsiqueira]

Yes, this also works for my use case. I'll try this change on the nls branch, and if it looks good I'll refactor.

[abelsiqueira]

What I missed before is that these names are fairly common choices for variables, and thye would conflict.

nvar = nvar(nlp)
...
nvar(nlp) # error in the same scope

On the other hand, usually you would either have a single nvar, so no need to call nvar(nlp) again, or multiple nvar, in which case, you'd have to name it better.
The only really conflicting use case I found was

function FeasModel(nlp :: AbstractNLPModel; name::String = name(nlp))
  ...
end

in which case, name::String had to be changed.

Do you see this becoming a problem?

[abelsiqueira]

I was wrong, nvar = nvar(nlp) won't work inside a function.

foo(a) = a+1
function bar()
  foo = foo(2)
end
bar() # ERROR: UndefVarError: foo not defined

I think the best approach here would be create a descriptive function call, e.g. nvar = number_of_variables(nlp). But then, the meta cleanup should be done first.

[dpo]

How about get_nvar()? There's a long discussion here: JuliaLang/julia#16770

[abelsiqueira]

Not implementing as discussed in #237.