I really like Julia's dispatch mechanisms, type system and so on. I have found a number of different ways I use it to design libraries and programs. But it would be great with some patterns/ideas/feedback from more seasoned Julia programmers. What are your Julia Design Patterns?
A concrete situation that I have struggled somewhat with is how to best design in Julia for the situation where I have one main/default algorithms/set-of-behaviors+data but then with a multitude of small variations. Typically there is a large set of data and methods/functions that are the same for the whole class of things and there are only 1-4 functions/methods that need to change for each variation. An example from BlackBoxOptim ( https://github.com/robertfeldt/BlackBoxOptim.jl ) is where there is one type for DifferentialEvolution and then multiple different variants of DE where only 1-2 functions differ from the "base" DE one. I have found a few different "design patterns" for this situation but not sure what is the long-term best: 1. Have a few Function fields in the "base" (composite) type which are set up at construction time and that implements the variant-specific behaviors. This is simple and direct but feels a bit "un-Julia" since it does not really use the dispatch system. One also has to predict the variation points (here: function) upfront which might not be flexible enough. Also performance might suffer since the types of the function not known. 2. Have one XBase type which includes a field of an abstract XStrategy type where specific sub-types to XStrategy implements each variant by implementing variant-specific functionality. This seems fairly efficient, but again one has to predict more or less where the variations should happen since the functions on the XBase type need to call to the XStrategy functions. 3. Have one XBase type which is then included as a field in specific variants. This seems efficient and flexible but the code is somewhat cluttered in that one has to have one extra indirection when accessing common data/fields (this is a similar problem in 2 above though). 4. "Copy" the common data/fields of XBase into each specific variant. This is the most flexible and should have high performance but there seem to be a risk that bugs have to be changed in multile source code locations since it is a kind of "copy-paste reuse". Would be great to hear your advice/feedback on how you design in/with the Julia type and dispatch system. Thanks, Robert Feldt
