title: How can I set default parameters for mutable structs in Julia?
body: <p>Is there a way to add default parameters for mutable structs in Julia?</p>
  <p>I'm trying to write something like the following:</p>
  <pre><code>mutable struct Scale
      # Set default values that will be changed by fit!()
      domain_min::Float64 = 0.0
      domain_max::Float64 = 1.0
      range_min::Float64  = 0.0 
      range_max::Float64  = 1.0
  end
  
  function fit!(data::Array)
      # Set struct params here using `data`
  end
  </code></pre>
  <p>Is there a way to do this or should I try a different approach?</p>