DataLength protocol defines a function to retrieve the length of data for various data types. Implemenations of this protocol need to implement len(data) function.

Default Implementations

The protocol provides default implementations for the following data types:

• String: Returns the number of graphemes in the string.
• List: Returns the number of elements in the list.
• Map: Returns the number of key-value pairs at the first level of the map.
• Tuple: Returns the number of elements in the tuple.
• Integer: Returns the number of digits in the integer plus 1 for a minus sign if the number is negative.
• Float: Returns the number of digits in the float plus 1 for a minus sign if the number is negative and 1 for a ".".

Default implementations examples:

BitString implementation returns the number of graphemes:

iex> DataLength.len("Hello! Dzień dobry!")
19

List implementation returns the number of elements in the list.

iex> DataLength.len(["a", :b, ["c"], %{d: "d"}])
4

Map implementation returns the number of key-value pairs at the first level of the map.:

iex> DataLength.len(%{a: 1, b: [2], c: "hello"})
3

Tuple implementation returns the number of elements in the tuple:

iex> DataLength.len({"a", :b, ["c", "d"], {"e"}, "f"})
5

Integer implementation returns the number of digits in the integer plus 1 for a minus sign if the number is negative:

iex> DataLength.len(1234567890)
10

iex> DataLength.len(-1234567890)
11

Float implemantation returns the number of digits in the float plus 1 for a minus sign if the number is negative and 1 for a ".". Terminal zeros in fractional part are ignored:

iex> DataLength.len(12345.6789)
10

iex> DataLength.len(12345.67890)
10

iex> DataLength.len(12345.67899)
11

iex> DataLength.len(-12345.67890)
11

iex> DataLength.len(-12345.67899)
12

Custom implementation:

You can implement custom length calculations for other data types by providing specific protocol implementations.

Example

  defmodule MyStruct do
    defstruct data: [1, 2, 3]
  end

  defimpl Length, for: MyStruct do
    def len(%MyStruct{data: data}), do: length(data)
  end