Writing comments

Instructions

• Standalone comments MUST be full sentences, starting with a capital letter and ending with a period.

  BAD
  // Start dispatcher
  
  GOOD
  // Start the dispatcher.
  

• Inline comments (appearing at the end of a line of code) SHOULD be fragments starting with a lowercase letter

  BAD
  eventChan chan *Event // Channel for events
  
  GOOD
  eventChan chan *Event // channel for events
  

• If an inline comment has to become multi-line, it MUST be converted to a standalone comment, and become a full sentence.

  BAD
  eventChan chan *Event // channel for events
                        // received from the network
  
  GOOD
  // Channel for events received from the network.
  eventChan chan *Event
  

• Multi-line comments MUST use //, not /* ... */.

  BAD
  /*
   This is a multi-line comment.
   It uses block comment syntax.
  */
  
  GOOD
  // This is a multi-line comment.
  // It uses line comment syntax.
  

• Apply semantic line breaks formatting to long comments.

• Avoid unnecessary comments that do not add value. See Avoid unnecessary comments below.

• When available, explain the "why" behind non-obvious code, not just the "what".

  BAD
  // Start workers.
  for i := 0; i < numWorkers; i++ {
      go worker()
  }
  
  GOOD
  // Workers must be spawned before sending the first event
  // or there will be a deadlock.
  for i := 0; i < numWorkers; i++ {
      go worker()
  }
  

Language-Specific Guidelines

Go

When writing comments for exported functions, types, or variables in Go, ALWAYS use the GoDoc style, starting with the name of the item being documented.

BAD
// This function starts the dispatcher.
func StartDispatcher() { ... }

GOOD
// StartDispatcher starts the dispatcher.
func StartDispatcher() { ... }

Avoid unnecessary comments

Do not add comments that do not add value. Consider:

• Is the code self-explanatory? If yes, DELETE the comment.

• Does the comment just restate what the code does? If yes, DELETE the comment.

• Is the comment out of date or incorrect? If yes, UPDATE or DELETE the comment.

Examples of comments to DELETE:

// Close the channel
close(ch)

// Start the worker
go worker()

// Increment counter
count++

Examples of comments to KEEP:

// Workers must be spawned before sending the first event
// or there will be a deadlock.
for i := 0; i < numWorkers; i++ { go worker() }

// Use a nil channel to disable this select case when buffer is empty.
processChan = nil

The key insight is:

• Comments are NOT there to narrate the code.
• Comments are there to:
  • provide additional context and explanation that is not obvious from the code itself
  • for large code blocks, allow readers to quickly grasp the intent without reading every line of code.