How to pass a function as a parameter in Lua?

Question

Bit confused by all this; so here's what I am attempting to do! Have a def thus:

block_basic_DEF =
{
    image = "button.png",
    name = "basic block",
    obj_table = this_obj_table.common_objects_table,
    startup = function() init(), <----- This is the problem
}

In another file I access as one would expect with:

function spawn(params)
    local obj = display.newImage(params.image)
    -- etc.

In that block_basic_DEF I wish to pass the address of the init() function such that in my spawn I can do something like:

params.startup() --i.e. actually call the original init function

Answer 1

Lua functions are just values, and you can asssign them using their name without parens:

function init() 
     print("init");
end

block = { 
     startup = init
}

And then call it like a regular function

block.startup()

It is near to OOP, but in fact it's as simple as the fact that a function is a normal value.

If you wanted something more similar to a lambda, you have to spell out the whole function, omitting the name:

startup = function() print("init") end

Answer 2

You just forgot the end keyword. It is part of a function definition and you can not leave it out. You wouldn't leave out the closing } in C either right?

block_basic_DEF =
{
    image = "button.png",
    name = "basic block",
    obj_table = this_obj_table.common_objects_table,
    startup = function() init() end, -- <-- This was the problem
}

Apart form that, the following two syntax variations are equal:

function foo()
end

foo = function()
end