Add write_to_file and read_from_file

[odow]

Closes #1075
Closes #1982

cc @dourouc05

[mlubin]

My only concern is that we're not following the standard Julia API by allowing reading and writing from an IO object. It's inevitable that we'll get requests for this. Does MOF support writing to streams?

[dourouc05]

Looks good to me (even though the failures on Windows are quite strange). Maybe refactor a bit the test suite to avoid having three times the exact same model? (Sorry for the delay, I still have the tab for my PR opened, but had too little time to work on it, unfortunately :(.)

I think this API is already quite good as it is. For streams, I suspect write and read overloads should be provided, but these cannot support the convenient inference from file name. This calls for a slightly different interface, like read/write(io::IO, m::Model, compression, format).

Another though: wouldn't the order format-compression for the arguments be easier to grasp? The file names almost invariably have first the file format, then the compression format (like .lp.gz).

Considering documentation, copying parts of MOF here really makes sense from a user point of view. However, if a format is added to MOF, it will require a manual modification of JuMP's doc: isn't there any other solution, like including parts of MOF docs from JuMP?

[codecov]

Codecov Report

Merging #2114 into master will increase coverage by 0.07%.
The diff coverage is 92.85%.

@@            Coverage Diff             @@
##           master    #2114      +/-   ##
==========================================
+ Coverage   91.01%   91.08%   +0.07%     
==========================================
  Files          40       41       +1     
  Lines        4350     4376      +26     
==========================================
+ Hits         3959     3986      +27     
+ Misses        391      390       -1

Impacted Files	Coverage Δ
src/JuMP.jl	80.98% <0%> (ø)	⬆️
src/file_formats.jl	100% <100%> (ø)
src/copy.jl	91.3% <100%> (+0.82%)	⬆️
src/print.jl	86.18% <0%> (+0.36%)	⬆️

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[odow]

Does MOF support writing to streams?

I've added the read/write to streams.

isn't there any other solution, like including parts of MOF docs from JuMP?

Longer term, we should probably pull MOF into MOI. Our longer term goal is to unify the JuMP/MOI documentation in a nice way.

[dourouc05]

Longer term, we should probably pull MOF into MOI. Our longer term goal is to unify the JuMP/MOI documentation in a nice way.

Nice to hear!

I've added the read/write to streams.

Why aren't you using the "standard" way of defining IO operations on streams (with read and write methods)? This would also imply to have the IO stream as a first argument, but would be more convenient for people picking up JuMP after Julia.

[odow]

Why aren't you using the "standard" way of defining IO operations on streams (with read and write methods)?

Mainly to keep consistency with write_to_file and read_from_file. It's a small change to swap filename to io. I'll defer to @mlubin if he prefers read/write though.

[mlubin]

I don't see the point of keeping consistency with write_to_file for the IO version. An IO isn't necessarily a file, so the name is misleading. I prefer using read and write with the argument order that's standard in Julia (https://docs.julialang.org/en/v1/manual/style-guide/#Write-functions-with-argument-ordering-similar-to-Julia-Base-1).

[odow]

I'm making changes to MathOptFormat.jl which should simplify JuMP's implementation. See: odow/MathOptFormat.jl#100.

[odow]

I've merged and released the changes to MathOptFormat.jl, so now things are now considerably simpler on the JuMP side.