Skip to content

Dependency Injection (Props)

The Props struct is the "Context Object" of GTB. It acts as a dependency injection container that carries global state, service interfaces, and tool metadata throughout your application's lifecycle.

What's in a Name?

The name Props is not merely a shorthand for 'properties' (though we do shove plenty of those in there). It’s a direct reference to a prop, the heavy-duty timber or steel beam that prevents a structure from an embarrassing collapse. For the sports fans, it’s also a lovingly crafted nod to the rugby position: the broad-shouldered stalwarts who provide the primary structural support for the scrum. Much like its on-field namesake, our Props struct isn't here to score the flashy tries; it's here to do the unsung heavy lifting that keeps the entire framework from falling over.

The Props Struct

Defined in pkg/props, the Props object typically contains:

  • Tool: Metadata about your CLI (Name, Summary, GitHub Org/Repo).
  • Logger: A unified logger abstraction (logger.Logger) with charmbracelet as the default backend for consistent output.
  • Config: The loaded configuration container.
  • FS: An abstraction of the file system (spf13/afero), allowing for easy mocking.
  • Assets: A manager for embedded filesystem resources.
  • Version: Current build information (Version, Commit, Date).
  • ErrorHandler: A centralized handler for fatal and non-fatal errors.

Why use Props?

Instead of using global variables or passing dozens of arguments to every function, you pass the Props object. This provides several key benefits:

  1. Testability: You can easily swap out the FS for an in-memory filesystem or provide a mock Logger during tests.
  2. Consistency: Global flags like --debug automatically update the Logger level inside Props, ensuring all components behave consistently.
  3. Extensibility: Adding new global services to the framework only requires adding them to the Props struct.

Usage in Commands

Every command constructor in GTB accepts *props.Props:

func NewCmdExample(p *props.Props) *setup.Command {
    return setup.Wrap("example", &cobra.Command{
        Use: "example",
        RunE: func(cmd *cobra.Command, args []string) error {
            p.Logger.Info("Hello from Props!")
            // Use p.FS to read a file
            // Use p.Config to get a value
            return nil
        },
    })
}