Appendix.md

Appendix

Identifiers vs expressions vs statements

A simplified explanation of the difference between identifiers, expressions and statements is,

• identifiers are names of things
• expressions are things that have values (you can pass these into functions), or refer to types
• statements are instructions to do things

Consider the following snippet.

var bar Bar
if err := foo(bar.Baz()); err != nil {
  return err
}

It contains,

• identifiers: err, foo, bar, Bar, Baz

  var bar Bar
      '-' '-'
  if err := foo(bar.Baz()); err != nil {
     '-'    '-' '-' '-'     '-'
    return err
           '-'
  }
  

• expressions: Bar, bar.Baz, bar.Baz(), foo(bar.Baz()), err, nil, and err != nil

  var bar Bar
          '-'
                .-------.
            .---|-------|.  .---------.
  if err := foo(bar.Baz()); err != nil {
                '-'   |     '-'    '-'
                '-----'
    return err
           '-'
  }
  

  Note that bar in var bar Bar is not an expression.

• statements: var ..., err := ..., if ..., and return ...

  var bar Bar
  '---------'
  if err := foo(bar.Baz()); err != nil {  -.
     '-------------------'                 |
    return err                             |
    '--------'                             |
  }                                       -'