Decimal.to_integer strangeness

Questions & Help Questions
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3

I did my experiment by copy and paste:

defmodule MyDecimal do
  # `to_integer/1` is copied from the source code of `Decimal`,
  # and added some `IO.inspect`

  def to_integer(%Decimal{sign: sign, coef: coef, exp: 0} = d)
      when is_integer(coef) do
        IO.inspect(d, label: "Branch 1", structs: false)
        sign * coef
      end

  def to_integer(%Decimal{sign: sign, coef: coef, exp: exp} = d)
      when is_integer(coef) and exp > 0 do
        IO.inspect(d, label: "Branch 2", structs: false)
        to_integer(%Decimal{sign: sign, coef: coef * 10, exp: exp - 1})
      end

  def to_integer(%Decimal{sign: sign, coef: coef, exp: exp} = d)
      when is_integer(coef) and exp < 0 and Kernel.rem(coef, 10) == 0 do
        IO.inspect(d, label: "Branch 3", structs: false)
        to_integer(%Decimal{sign: sign, coef: Kernel.div(coef, 10), exp: exp + 1})
      end
end

MyDecimal.to_integer(Decimal.new("1234.50"))

and it prints

Branch 3: %{__struct__: Decimal, coef: 123450, exp: -2, sign: 1}

** (FunctionClauseError) no function clause matching in MyDecimal.to_integer/1

The following arguments were given to MyDecimal.to_integer/1:

    # 1
    #Decimal<1234.5>

    #cell:2: MyDecimal.to_integer/1

So, the “problem” occurs when trying to do to_integer(%Decimal{sign: 1, coef: 12345, exp: -1}).

Maybe Decimal does not want you to do anything ambiguous about the fraction part.