A package is a folder that contains a bunch of go files, a bunch of packages is known as a module, defined by a go.mod file.

• A package is a directory inside your $GOPATH/src directory containing, amongst other things, .go source files.
• Package names should be all lower case and only letters.

All the files in a package’s directory must have the same package declaration.

You can pick almost any string as your module path but focus on uniqueness to avoid potential import conflict with other people’s projects or the standard library in the future.

• You want to pick a path that is globally unique, a common convention is to base your module paths on a URL that you own.

  app.hamada.com
  

You can view Go's packages documentations using go doc package-name (e.g., go doc fmt).

Package main will only contain integration of other packages and not unit-testable code.

Go is good for tooling because it is simple with syntax that is easy to parse, built-in packages for parsing + formatting code, and has tools like gofmt, godoc, and gofix because of this design.

Go uses naming conventions to control visibility (exported vs unexported identifiers):

• Identifiers that start with an uppercase letter are exported (public) and can be accessed from other packages.
• Identifiers that start with a lowercase letter are unexported (private to the package they are defined in).
• This applies to variables, constants, functions, methods, structs, interfaces, and fields.

package wallet

type Wallet struct {      // exported
    balance int          // unexported
}

func (w *Wallet) Deposit(amount int) {} // exported
func (w *Wallet) reset() {}             // unexported

• Code in another package can use Wallet and Deposit, but cannot access balance or call reset.

• Go does not have public or private keywords; capitalization determines visibility.

• To access exported identifiers from another package, import the package and reference them using dot notation:

  package main
  
  import "example/wallet"
  
  func main() {
      w := wallet.Wallet{} // OK: Wallet is exported
  
      w.Deposit(100)       // OK: Deposit is exported
  
      // w.balance = 100   // ERROR: balance is unexported
      // w.reset()         // ERROR: reset is unexported
  }