Type instability of nested function

New to Julia
2

I guess you hit performance of captured variables in closures · Issue #15276 · JuliaLang/julia · GitHub

Current solution is just to put your closure in let block

function test(a)
    b = a
    if a < 0
        b = -a
    end
    let b = b
        f(x) = x + b
        f(10)
    end
end

julia> @code_warntype test(1)
MethodInstance for test(::Int64)
  from test(a) in Main at REPL[3]:1
Arguments
  #self#::Core.Const(test)
  a::Int64
Locals
  b@_3::Int64
  f::var"#f#4"{Int64}
  b@_5::Int64
Body::Int64
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