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Ever wanted to read Configurations.jl from environment variables? Here you go 🙂

using Configurations
@option struct Opt1
    b::Union{Nothing, Int} = nothing
@option struct Opt2

using ConfigurationsENV

# without an explicit `env` argument to `from_env`, the global `ENV` is used
env = Dict(
    "PREFIX_A_A" => "true",
    "PREFIX_A_B" => "",
    "PREFIX_B" => "hello world",

config = from_env(Opt2, env, prefix="PREFIX_", separator="_")  
# Opt2(Opt1(true, nothing), "hello world")

to_env(config, prefix=">")  # separator defaults to "__", prefix to ""
# OrderedCollections.OrderedDict{String, Any} with 3 entries:
#   ">A__A" => true
#   ">A__B" => nothing
#   ">B"    => "hello world"

In case you just want to parse a subset of the options fields from environment variables, use return_dict=true.

env = Dict("PREFIX__A__A" => "true")

nested_dict = from_env(Opt2, env, prefix="PREFIX__", return_dict=true)
# DataStructures.DefaultDict{String, Any, typeof(ConfigurationsENV.RecursiveDict)} with 1 entry:
#   "a" => DefaultDict{String, Any, typeof(RecursiveDict)}("a"=>true)

This dict can then be merged with other sources of parameters like TOML files or dicts.

from_dict(Opt2, merge(nested_dict, Dict("b" => "works")))
# Opt2(Opt1(true, nothing), "works")