I am learning Lua and came across the following construct:
button.action = function() buttonPressed() end Is it the same as
button.action = buttonPressed() end ?
I understand that button.action is assigned a value returned by buttonPressed(), but why wrap it into anonymous function like that?
This:
button.action = function() buttonPressed() end is (almost) the same thing as this:
button.action = buttonPressed But note the absence of parentheses at the end.
As @hjpotter92 said, the main difference is that buttonPressed could return something whereas button.action does not.
buttonPressed's value, the latter will not depend."I understand that button.action is assigned a value returned by buttonPressed(), but why wrap it into anonymous function like that?"
You got it wrong. The statement:
button.action = function() buttonPressed() end assigns to button.action an anonymous function that, when called, will in turn perform the call buttonPressed(). Note that the anonymous function doesn't return anything, so it is called only for its side effects. This is a common idiom with callbacks. You use an anonymous function to delay the execution of some piece of code (in this case, only the call to buttonPressed) until you need to execute it.
Given the names of your snippet I guess that this code sets the action to be performed when some button is pressed. When the button is pressed, then the action is fired (somewhere in the bowel of the code there will be a call like button.action() that calls the anonymous function stored in button.action) and the call buttonPressed() is performed.
Lua on its own has no concept of private/protected variables. Various programmers use various methods to emulate the same result.
As for your interpretation of the construct; there is a mismatched end statement. Even ignoring that syntactical error, the value of button.action will not be that returned by buttonPressed function. Here's a small demonstration to show you:
x = function() return 'hi' end y = function() x() end z = x() print( y, z, y(), 1 ) As you can see, it's most probably the programmer's way to incorporate a "protected" function or class (in my opinion).
endfor closing a block scope but nothing starting it. Are you sure that's the full code?