UsingMerge: merge method definitions when using a package

This package (now registered) exports a single macro @usingmerge which differs from
using in that it “merges” the exported definitions automatically.

The wish for this started in
this thread.
At the time I was very new to Julia and did not think I could do anything
myself about the problem. Two years later, knowing better Julia, I realized
I could do something. Here it is.

I introduce the problem with an example.

In my Gapjm package (a port of some GAP libraries to Julia) I have a
function invariants which computes the invariants of a finite reflection
group. However when I use BenchmarkTools to debug for performance my
package, I have the following problem:

julia> G= # some group...

julia> invariants(G)
WARNING: both Gapjm and BenchmarkTools export "invariants"; uses of it in module Main must be qualified
ERROR: UndefVarError: invariants not defined
Stacktrace:
 [1] top-level scope at REPL[4]:1
 [2] eval(::Module, ::Any) at ./boot.jl:331
 [3] eval_user_input(::Any, ::REPL.REPLBackend) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.4/REPL/src/REPL.jl:86
 [4] run_backend(::REPL.REPLBackend) at /home/jmichel/.julia/packages/Revise/kqqw8/src/Revise.jl:1163
 [5] top-level scope at none:0

This is annoying! I do not want to have to qualify every call to my
function invariants just because I am timing my code! What can I do?
Well, first I could just import the methods I am using in BenchmarkTools:

julia> using BenchmarkTools: @btime

Actually, every exported name from BenchmarkTools, except invariants,
does not conflict with my code:

julia> names(BenchmarkTools)
30-element Array{Symbol,1}:
 Symbol("@ballocated")
 Symbol("@belapsed")
 Symbol("@benchmark")
 Symbol("@benchmarkable")
 Symbol("@btime")
 Symbol("@tagged")
 :BenchmarkGroup
 :BenchmarkTools
 :addgroup!
 :allocs
 :gctime
 :improvements
 :invariants
 :isimprovement
 :isinvariant
 :isregression
 :judge
 :leaves
 :loadparams!
 :mean
 :median
 :memory
 :params
 :ratio
 :regressions
 :rmskew
 :rmskew!
 :trim
 :tune!
 :warmup

so I can do:

julia> using BenchmarkTools: @ballocated, @belapsed, @benchmark, @benchmarkable, @btime, @tagged, BenchmarkGroup, BenchmarkTools, addgroup!, allocs, gctime, improvements, isimprovement, isinvariant, isregression, judge, leaves, loadparams!, mean, median, memory, params, ratio, regressions, rmskew, rmskew!, trim, tune!,
 warmup

Still no conflict. Can I go further and do something even for invariants?
Well, I have one method for invariants in my package:

invariants(a::Group, args...)

while BenchmarkTools has four:

invariants(group::BenchmarkGroup)
invariants(x)
invariants(f, group::BenchmarkGroup)
invariants(f, x)

Even though some of these last methods apply to Any, they do not conflict
with my method (since at least one of the arguments of my method, the
first, is qualified with my type Group), so I can use them also by just
defining:

invariants(group::BenchmarkGroup) = BenchmarkTools.invariants(group)
invariants(x) = BenchmarkTools.invariants(x)
invariants(f, group::BenchmarkGroup) = BenchmarkTools.invariants(f, group)
invariants(f, x) = BenchmarkTools.invariants(f, x)

The last thing to do is make the docstring of BenchmarkTools.invariants
accessible to the help of invariants. It happens it has no docstring, but
if it had one I must do (this adds to the doc of invariants):

@doc (@doc BenchmarkTools.invariants) invariants

I call the end result of the above process merging the package
BenchmarkTools with my current package. What I announce here is a
macro @usingmerge which does all the above automatically. If you do

julia> using UsingMerge
julia> @usingmerge BenchmarkTools

The function determines conflicting method names in the package and merges
them as above, and does using of the non-conflicting names.

Just like for using you can usingmerge only some of the names of the
package

julia> @usingmerge BenchmarkTools: invariants, ratio

The macro @usingmerge has two optional arguments

julia> @usingmerge reexport BenchmarkTools

will reexport all non-conflicting names (a conflicting name is by
definition already present in your environment and will be exported if you
did export it).

julia> @usingmerge verbose=true BenchmarkTools

will print all conflicts resolved, and verbose=2 will print all executed
commands.

You will find some more information in the docstring of @usingmerge.

Since I wrote this function, I found that I got the hoped for modularity
benefits in my code. For example, I have in my Gapjm.jl package modules

  • Perms Permutations
  • Cycs Cyclotomic numbers (sums of complex roots of unity)
  • Pols Univariate Laurent polynomials
  • Mvps.jl Multivariate Puiseux polynomials
  • Posets.jl Posets
  • FFields.jl Finite fields

that I designed as independent, stand-alone packages which each can be used
without importing anything else from my package. To use them together I can
now just using_merge each of them instead of writing (unpleasant) glue
code.

I do not advocate always replacing the semantics of using with that of
@usingmerge, but I feel that @usingmerge is a nice tool for using
packages together without having to write glue code (and without having to
modify any of the used packages). The meaning of “pirating a type” becomes
a little bit wider in this context, as you saw with the method
invariants(y) in BenchmarkTools: it is, I would say, polite, if any of
your methods which has a possibly conflicting name uses at least one of
your own types in its signature.

The program only merges methods of functions. If a conflicting name is a
macro, a struct or a type, a message is printed and the name is not
merged.

Any kind of feedback will be welcome. My implementation is perhaps not the
best, as I kind of parse the printed output of methods. Accessing the
internal structure of the returned object would be better but I do not know
what’s officially accessible in there. If you have any comments on the
code, functionality or documentation please contact me.

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