ruby 46 lines · 7 steps

Typed environment variable config in Ruby

A module reads environment variables and coerces them into typed, validated config values with sensible defaults.

Explained by highlit
Intermediate environment-variables type-coercion configuration error-handling module-functions
1module AppConfig
2 module_function
3 
4 def fetch(key, default: nil, required: false)
5 value = ENV[key]
6 if value.nil? || value.strip.empty?
7 raise KeyError, "Missing required env var: #{key}" if required
8 return default
9 end
10 value
11 end
12 
13 def integer(key, default: nil, required: false)
14 raw = fetch(key, default: nil, required: required)
15 return default if raw.nil?
16 Integer(raw)
17 rescue ArgumentError
18 raise ArgumentError, "Env var #{key} must be an integer, got #{raw.inspect}"
19 end
20 
21 def float(key, default: nil, required: false)
22 raw = fetch(key, default: nil, required: required)
23 return default if raw.nil?
24 Float(raw)
25 rescue ArgumentError
26 raise ArgumentError, "Env var #{key} must be a float, got #{raw.inspect}"
27 end
28 
29 def boolean(key, default: false)
30 raw = fetch(key)
31 return default if raw.nil?
32 %w[1 true yes on].include?(raw.strip.downcase)
33 end
34 
35 def list(key, default: [], separator: ",")
36 raw = fetch(key)
37 return default if raw.nil?
38 raw.split(separator).map(&:strip).reject(&:empty?)
39 end
40 
41 DATABASE_URL = fetch("DATABASE_URL", required: true)
42 POOL_SIZE = integer("DB_POOL", default: 5)
43 TIMEOUT = float("REQUEST_TIMEOUT", default: 30.0)
44 DEBUG = boolean("DEBUG", default: false)
45 ALLOWED_HOSTS = list("ALLOWED_HOSTS", default: ["localhost"])
46end
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Centralizing env access behind one module gives you a single place to validate and coerce configuration.
  2. 2Coercing raw strings into integers, floats, booleans, and lists catches misconfiguration at boot instead of deep in the app.
  3. 3Raising descriptive errors for missing or malformed values turns silent misconfiguration into loud, actionable failures.

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