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In a Package I am writing, I'm trying to define a function with an Optional parameter in it that is set to a global variable.


However, the Optional value IndexLoopPlot is not set until after the package is loaded and other functions are run. Therefore PlotIndex is read in as,


In other words, IndexLoopPlotMtx is set to Null, and when the function is run later it tries to plot {} instead of the matrix IndexLoopPlot. Is there a way to get it delay setting the Default until the function is called for the first time from the package?

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1 Answer

You'll have to point to the global variable using its full context path as Global`IndexLoopPlot. Otherwise, the optional variable will be interpreted as YourPackage`IndexLoopPlot. The following example shows how:

Quiet@Remove[a, "test`*"];
f[x_: Global`a] := {x}

enter image description here

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