How to write a function that outputs the linear combination of other functions?

General Usage
3

No new type needed. You can also get type-stable code with:

linear_combinations(f, c) = (x...; kw...) -> map(c, f) do c, f
    c*f(x...; kw...)
end |> sum

Defining new callable types (“functors”) can be useful for other reasons, of course; see How are functors useful? - #6 by stevengj

The trick here is that you construct tuples from tuples (map has specialized methods for tuples), rather than generators foo for (c, f) in zip(...). I believe zip by itself is also type-unstable for heterogeneous tuples, for that matter.

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