PITCHME.md

Settings

A clean way to handle custom configuration values

In any Ruby app (not only Rails)

And without using method_missing

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Convoluted custom configuration chaos

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What's the value when and why?

• does it use the dot-env file ENV variable?
• does it use the Docker ENV variable?
• does it use the server set ENV variable?
• what is the load order of initializers?

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Don't use ENV in your apps directly

• rely on configuration values set in your code
• don't fail silently on typos
• use default values
• use objects, not only strings

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No external dependency

• setting values is simple
• no need to add another gem to your codebase
• use the same mechanism regardless of the environment

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Everything in one file

• keep the overview
• understand the mechanism
• add custom methods easily
• load it before anything else

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Implementation

There is not much code to show, so I will show it.

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Settings.register

# class Settings
#
def self.register(var_name)
  define_singleton_method(var_name) {
    instance_variable_get("@#{var_name}")
  }

  instance_variable_set("@#{var_name}",
    ENV.fetch(var_name.to_s.upcase))
end

---

Settings.register with default value

# class Settings
#
def self.register(var_name, default: nil)
  define_singleton_method(var_name) {
    instance_variable_get("@#{var_name}")
  }

  instance_variable_set("@#{var_name}",
    ENV.fetch(var_name.to_s.upcase, default))
end

---

Settings.register usage

# Set custom configuration variable with default:
#
# uses default unless ENV["API_URL"] is set
#
register :api_url, default: "http://localhost:4567/api"

# Access:
#
Settings.api_url

---

Settings.register with default value

# class Settings
#
def self.register(var_name, default: nil)
  define_singleton_method(var_name) {
    instance_variable_get("@#{var_name}")
  }

  instance_variable_set("@#{var_name}",
    ENV.fetch(var_name.to_s.upcase, default))
end

---

Settings.set extracted

# class Settings
#
def self.register(var_name, default: nil)
  define_singleton_method(var_name) {
    instance_variable_get("@#{var_name}")
  }

  set(var_name, ENV.fetch(var_name.to_s.upcase, default))
end

def self.set(var_name, value)
  instance_variable_set("@#{var_name}", value)
end

---

Settings.set usage

# overwrite registered variables:
#
Settings.set :access_locked, true

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Avoid comparison bugs

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Do you spot the classic error?

if ENV["PRINT_STACKTRACE"]
  # ...

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What if...?

export PRINT_STACKTRACE=false

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Type agnostic comparison method

def self.is?(var_name, other_value)
  public_send(var_name.to_sym).to_s == other_value.to_s
end

if Settings.is?(:print_stacktrace, true)
  # ...

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Convoluted custom configuration chaos

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Consistent concise custom configuration

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Consistent concise custom configuration

• all custom configuration values are declared in one file
• the code is easily grep-able for their usage
• load order is clear
• use the same mechanism regardless of the framework

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Code examples

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Thank you

 

Find this presentation

and several code examples

under: https://github.com/mediafinger/settings

 

Andreas Finger     @mediafinger