Feature flags in Go

Flag type and constants

Define flags as a typed string constant in your domain or feature package — never raw strings at call sites:

type Flag string

const (
    FlagDarkModeEnabled    Flag = "dark_mode_enabled"
    FlagNewCheckoutEnabled Flag = "new_checkout_enabled"
)

Keep all flag constants in one file so adding a flag is a single-location diff.

Evaluator interface