What are mutating functions in Julia?

The concept of mutating functions in Julia is straightforward. A mutating function changes the contents of an array/vector. These functions’ names are suffixed with !.

Note: If the function changes the array reference without changing its content, it’s not a mutating function.

Coding example

Refer to the following example to understand a mutating function. In this example, we’ll create a function that halves every value of the passed vector in place, thus changing the contents of the vector.

function half_each_array_val!(v::Vector{Float64})
    for ind in eachindex(v)
        v[ind] = v[ind] / 2
    end
end
vec = Vector{Float64}([3, 15, 21, 94])
println("Original Vector:")
println(vec)
half_each_array_val!(vec)
println("\nMutated Vector:")
println(vec)

Explanation

  • Lines 1–5: We define a function named half_each_array_val!(), which accepts a vector of type float64. It will halve every value in the provided vector.
  • Line 7: We define a vector of float values named vec.
  • Line 9: We print the original vector.
  • Line 10: We invoke the half_each_array_val!() function with vec as the argument.
  • Line 12: We print the mutated vector.

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