Elixir v1.4.5 Inspect protocol View Source
The Inspect
protocol is responsible for converting any Elixir
data structure into an algebra document. This document is then
formatted, either in pretty printing format or a regular one.
The inspect/2
function receives the entity to be inspected
followed by the inspecting options, represented by the struct
Inspect.Opts
.
Inspection is done using the functions available in Inspect.Algebra
.
Examples
Many times, inspecting a structure can be implemented in function
of existing entities. For example, here is MapSet
’s inspect
implementation:
defimpl Inspect, for: MapSet do
import Inspect.Algebra
def inspect(dict, opts) do
concat ["#MapSet<", to_doc(MapSet.to_list(dict), opts), ">"]
end
end
The concat/1
function comes from Inspect.Algebra
and it
concatenates algebra documents together. In the example above,
it is concatenating the string "MapSet<"
(all strings are
valid algebra documents that keep their formatting when pretty
printed), the document returned by Inspect.Algebra.to_doc/2
and the
other string ">"
.
Since regular strings are valid entities in an algebra document, an implementation of inspect may simply return a string, although that will devoid it of any pretty-printing.
Error handling
In case there is an error while your structure is being inspected,
Elixir will raise an ArgumentError
error and will automatically fall back
to a raw representation for printing the structure.
You can however access the underlying error by invoking the Inspect implementation directly. For example, to test Inspect.MapSet above, you can invoke it as:
Inspect.MapSet.inspect(MapSet.new, %Inspect.Opts{})