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');
   (require 'glass.error'); -- Throw error if nothing matches
})
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. (requires cjson)
• 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. (requires lyaml)
• error pseudo-loader that throws an error.

* 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.

Note that some of these loaders require additional dependencies that are not included with glass to keep the installation small.

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.