Question

I am learning Lua and have come across the concept of anonymous functions. It’s interesting but I was wondering what additional advantage it provides over non anonymous functions.

So If I have something like

function(a,b) return (a+b) end

The function is anonymous and if I have

function add(a,b) return (a+b) end

The function is non anonymous. The second is better because I can call it wherever I want and I also know what my function is doing. So what’s the advantage of anonymous functions? Am I missing something here?

Answer 1

To be honest, there is no such thing as a named function in Lua. All functions are actually anonymous, but can be stored in variables (which have a name).

The named function syntax function add(a,b) return a+b end is actually a syntactic sugar for add = function(a,b) return a+b end.

Functions are often used as event handlers and for decisions which a library does not/cannot know, the most famous example being table.sort() – using your function, you can specify the sorting order:

people = {{name="John", age=20}, {name="Ann", age=25}}
table.sort(people, function (a,b) return a.name < b.name end)

The point is that most probably you won’t need the function later. Of course, you can also save the function to a (possibly local) variable and use that:

local nameComparator = function (a,b) return a.name < b.name end
table.sort(people, nameComparator)

For more information, read this section on functions in PiL.