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Line, block and nested comments - Lua compared to other languages

You can comment your Lua program in two ways.

a) using comments that start -- , in which case they run to the end of the line - so that's a line comment

b) starting --[[ , in which case they run through to the next ]] which may be in the same line, or a number of lines later - so that's a block comment

Line and block comments are common in many other languages too
• in PHP, for example, a line comment starts with a # or //, and a block comment runs from /* to */.
• in C++ and in Java, line comments start with //, and block comments run from /* to */.
• ANSI C only supports block comments from /* to */, though some extended compilers accept line comments from //.
&bull, In Tcl, Perl and Python you have just line comment support from # to the end of the line
and in all the languages we teach, blank lines will be ignored too so are in effect a separating comment

One of the things I regret about block comments in most langauges is that they cannot be nested. In other words, you can't write a comment with a comment. "Does this matter?" you ask. Yes, it does to me ... I want to be able to comment out a whole block of code that's already got comments within it, and that's a problem where the end of the inner comment also forces the end of the outer comment. Lua (uniquely in the languages we teach) provides a solution in that block comments can start with extra = signs between the [ and [, and then the terminating sequeence need to have the same number of == signs ... so

  print ("This will be printed first")
  
  --[===[ Comment out a whole big block!
  
  --[[ This is a multiline comment telling you about
  the work this code is doing ]]
  
  print ("This will not be printed in the middle")
  
  --[[ This is another multiline comment telling you about
  the work this code is doing ]]
  
  end of big block comment ]===]
  
  print ("This will be printed last")


will just print out two lines, with the one in the middle being skipped.

Examples, in context - see [here].
(written 2014-05-04, updated 2014-05-06)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
U101 - Introduction to Lua.
  [4324] Learning to program - variables and constants - (2014-11-22)
  [3724] Learning to Program in Lua - public / open training course / class - (2012-05-09)
  [2310] Learning to write high quality code in Lua - (2009-07-30)
  [1842] Lua Course, and the Wiltshire Countryside too - (2008-10-16)
  [1737] Rules, suggestions, considerations for Lua variable names - (2008-08-05)
  [1699] If you are learning Lua, here are some more examples - (2008-07-06)
  [1695] Lua Course - here is the index - (2008-07-03)
  [1111] Training in Lua - (2007-03-16)


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