# booleans # simple: providing any value for ENV['FORCE_SSL'] means `true`: force_ssl = !!ENV['FORCE_SSL'] # more advanced: # only when we provide 'true' will `force_ssl` become true. force_ssl = ('true' == ENV['FORCE_SSL'])

It also makes it hard to centralize type coercions and default values.

It’s easy to create bugs because the environment is a somewhat degenerate settings database.

Most programming languages vend environment variables as strings. This leads to errors like so: