[markkitti]

Now with better formatting...

This becomes an important part of optimizing Julia code. There is some tooling for this. Below, identity is a type stable function because we know that an Int64 argument results in a Int64 output. The macro code_warntype reveals the type analysis:

  julia> @code_warntype identity(5)
  MethodInstance for identity(::Int64)
    from identity(x) in Base at operators.jl:526
  Arguments
    #self#::Core.Const(identity)
    x::Int64
  Body::Int64
  1 ─     return x


  julia> f(x) = identity(x ≥ 0 ? x : x + 0.0) 
  f (generic function with 1 method)

  julia> @code_warntype f(5)
  MethodInstance for f(::Int64)
    from f(x) in Main at REPL[6]:1
  Arguments
    #self#::Core.Const(f)
    x::Int64
  Locals
    @_3::Union{Float64, Int64}
  Body::Union{Float64, Int64}
  1 ─ %1 = (x ≥ 0)::Bool
  └──      goto #3 if not %1
  2 ─      (@_3 = x)
  └──      goto #4
  3 ─      (@_3 = x + 0.0)
  4 ┄ %6 = @_3::Union{Float64, Int64}
  │   %7 = Main.identity(%6)::Union{Float64, Int64}
  └──      return %7