Lua Configuration Syntax

Configuration Example
Function Syntax

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Lua Configuration Syntax

Configuration Example

Lapis' configuration module gives you support for merging tables recursively.

For example we might define a base configuration, then override some values in the more specific configuration declarations:

-- config.lua
local config = require("lapis.config")

config({"development", "production"}, {
  host = "example.com",
  email_enabled = false,
  postgres = {
    host = "localhost",
    port = "5432",
    database = "my_app"
  }
})

config("production", {
  email_enabled = true,
  postgres = {
    database = "my_app_prod"
  }
})

This results in the following two configurations (default values omitted):

-- "development"
{
  host = "example.com",
  email_enabled = false,
  postgres = {
    host = "localhost",
    port = "5432",
    database = "my_app",
  },
  _name = "development"
}

-- "production"

{
  host = "example.com",
  email_enabled = true,
  postgres = {
    host = "localhost",
    port = "5432",
    database = "my_app_prod"
  },
  _name = "production"
}

You can call the config function as many times as you like on the same configuration names, each time the passed in table is merged into the configuration.

Tables with named keys are merged key by key. Arrays are not merged: an array replaces any existing value, so setting {9} on top of {1, 2, 3} results in {9}, and setting {} clears the array. An error is thrown for a table with both array items and named keys, or an array with missing (nil) values.

Instead of a table, a function can be passed to config. Inside the function, calling a name as a function sets that value in the configuration. Passing a function as the value creates a nested table. This is the same syntax used by MoonScript configurations, and lets you add logic around your assignments:

-- config.lua
local config = require("lapis.config")

config("development", function()
  port(8080)

  if os.getenv("USE_SQLITE") then
    sqlite(function()
      database("my_app.sqlite")
    end)
  else
    postgres(function()
      database("my_app")
    end)
  end
end)

Names that are already global variables in Lua, like type or table, can’t be set this way because the global is found instead. Use set to assign them: set("type", "fast"). unset removes previously set values, eg. unset("email_enabled").

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