Glass

Makes your configs (almost) see-through.

About

Glass is a Lua library that makes it easy to lazy-load configuration files into a Lua table at runtime. Its main purpose is to make accessing different configuration files "transparent" to the programmer.

With Glass, you can index a key in an object in a JSON file in a subdirectory as if indexing a nested table.

As a side effect, it also decouples the code from the config format: your program doesn't need to care whether a specific configuration file is in YAML or JSON format as long as the structure is correct.

Example

Assume the file app/config/settings.json exists in your project directory with the content {"user":{"name":"User"}}

local glass = require 'glass'
local config = glass.bind('app/config', {
   (require 'glass.json');
})
print(config.settings.user.name) -- prints "User"

How it Works

A glass loader is initialised with a list of loaders and will try each of them in order in its __index metamethod. The first loader that is able to fetch the wanted configuration will be used.

Loaders

Glass offers the following loaders out of the box:

• cosmo loads cosmo templates
• discount loads markdown files*.
• environment loads environment variables.
• json loads a JSON file as a Lua table.
• lua loads and executes a Lua file.
• moonhtml loads a MoonHTML template and returns it as a function.
• readfile loads a file as a string.
• skooma loads a skooma template and returns it as a function.
• table looks up values in a Lua table
• yaml loads a YAML file as a Lua table.

* For easier interoperability with other template loaders, the discount loader returns a static function which can be called to return the generated HTML. The markdown file is only parsed the first time.

Custom Loaders

A glass loader is simply a Lua function that takes as its argument a path to a file and attempts to load it into a Lua value.

Loaders will typically add an extension to the given file name before checking whether that file exists and can be loaded.

When a loader cannot find the expected file, it should return nil to let glass continue the loader chain. When a loader returns a truthy value, this will be used and no further loaders will be tried.