# Use of anonymous functions has high compilation time

**URL:** <https://discourse.julialang.org/t/use-of-anonymous-functions-has-high-compilation-time/125923>\
**Category:** General Usage\
**Tags:** compilation, functions, anonymous-function\
**Created:** [February 14, 2025, 9:27pm UTC](https://discourse.julialang.org/t/use-of-anonymous-functions-has-high-compilation-time/125923 "2025-02-14T21:27:44Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![thomasc791](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/thomasc791/32/214650_2.png) [@thomasc791](https://discourse.julialang.org/u/thomasc791)\
**Post date:** [February 14, 2025, 9:27pm UTC](https://discourse.julialang.org/t/use-of-anonymous-functions-has-high-compilation-time/125923/1 "2025-02-14T21:27:44Z")

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Hi everyone,

I am currently struggling with the usage of anonymous functions. I have a function `dirichlet!` that takes a function as one of its inputs. The function returns a value based on the position `x`.

```julia
function dirichlet!(f, K::SparseMatrixCSC{Tv,Ti}, F::Vector{Tv}, nodes::Matrix{Tv}, elements::GFMat{<:Int}, axis::NTuple{N,<:Int}) where {Ti,Tv,N}
  dofAxes = Vector{Int}()
  for i in eachindex(axis)
    if axis[i] > 0
      push!(dofAxes, i)
    end
  end
  for i in axes(elements, 1)
    e = elements[i]
    for n in e
      dofs = dofAxes .+ (n - 1) * N
      x::Vector{Tv} = nodes[1:N, n]
      pval::NTuple{N,Tv} = f(x)
      _prescribef!(dofs, K, F, pval)
      _zerorow!(dofs, K)
      _zerocolumn!(dofs, K)
      K[dofs, dofs] .= 1.0
    end
  end
  dropzeros!(K)
  return F
end

```

However, when I actually use the function there is an almost 100% compilation time each time i run the code. If I set `pval` manually the compilation time goes back to 0%.

I run the code like this:

```julia
  fr = (::Vector{Float64}) -> (0.0, 0.0)
  F = dirichlet!(fl, K, F, mesh.nodes, left, (1, 0))

```

I have tried different methods of inputting the function, and changing the input type of function, but nothing seemed to work.

Any help would be greatly appreciated.

Kind regards,  
Thomas

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**Author:** ![gdalle](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/gdalle/32/27854_2.png) [@gdalle](https://discourse.julialang.org/u/gdalle)\
**Post date:** [February 14, 2025, 9:45pm UTC](https://discourse.julialang.org/t/use-of-anonymous-functions-has-high-compilation-time/125923/2 "2025-02-14T21:45:50Z")

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Your code isn’t reproducible (where does `GFMat` come from?) but I suspect you’re hitting the infamous [heuristic for avoiding specialization](https://docs.julialang.org/en/v1/manual/performance-tips/#Be-aware-of-when-Julia-avoids-specializing). When you pass a function `f` as argument to another function `g`, the compiler does not specialize the resulting code by default, which means it cannot infer what `f(x)` will be inside `g`. This also explains why setting `pval` manually resolves it. To force specialization, just add a type annotation `f::F` to the function signature. Does it work?

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<div class="post-metadata">

**Author:** ![thomasc791](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/thomasc791/32/214650_2.png) [@thomasc791](https://discourse.julialang.org/u/thomasc791)\
**Post date:** [February 14, 2025, 10:06pm UTC](https://discourse.julialang.org/t/use-of-anonymous-functions-has-high-compilation-time/125923/3 "2025-02-14T22:06:15Z")

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I already tried adding the type to the function, but that didn’t change a lot.

However, I realised that I was not really correctly benchmarking. The compilation time was almost 100% for low DOF problems, but for higher DOF problems the `_zerorow!` function is the bottleneck. My bad I should have check better before posting. Thanks anyways for helping.

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<div class="post-metadata">

**Author:** ![gdalle](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/gdalle/32/27854_2.png) [@gdalle](https://discourse.julialang.org/u/gdalle)\
**Post date:** [February 14, 2025, 10:17pm UTC](https://discourse.julialang.org/t/use-of-anonymous-functions-has-high-compilation-time/125923/4 "2025-02-14T22:17:58Z")

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Regardless of problem size, compilation time should account for exactly 0% after the first run, otherwise you have some type-instabilities. Did you use BenchmarkTools.jl for benchmarking? Did you interpolate the variables?