Using multiple dispatch in packages

General Usage
1

I need some clarification on how multiple dispatch (or “inheritance”) is working between packages. Let’s take CSVFiles for example.

I can run load("file.csv") and it returns a table. In the source code, we have export load, save yet I don’t see the load function defined anywhere. There are

function fileio_load(f::FileIO.File{FileIO.format"CSV"}, delim=','; args...)
    return CSVFile(f.filename, delim, args)
end

function fileio_load(f::FileIO.File{FileIO.format"TSV"}, delim='\t'; args...)
    return CSVFile(f.filename, delim, args)
end

and
function _loaddata(file) which i suppose is a helper function.

The homepage of CSVFiles says something about FileIO. I suspect the load() is defined somewhere in there… so what is the exact sequence of functions that are run when I type in load.

Moreover, suppose I am developing a package that can read a particular file and would also like to use load() in my package. Can I just have a signature load(::MyType)? Will this automatically “hook” into FileIO?

2

load is defined in FileIO. It’s one of the stranger examples of multiple dispatch, because we explicitly urge people not to extend this function, instead having FileIO call the module-specific version by scoping (e.g., CSV.load(args...)), so that the only methods defined for load are in FileIO itself and CSV.load is a nominally-unrelated function.

This is not how it typically works (in FileIO it seems necessary to allow multiple packages to implement different approaches for a single file format), so I’m not sure this is the best model for understanding how this typically works.

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