How to undraw something?

[Xgoff]

In Lua, you don't have to say == true

usually you don't, but yes you don't need this in general

i've tried ternary logic once or twice with events being called on objects, where you do want to make that distinction sometimes:

• e == true: event ran successfully
• e == false: event exists, but didn't run successfully
• e == nil: event doesn't exist

or without those specific checks then it just collapses into "did happen" or "didn't happen", which is also useful

could also be useful for certain types of configuration settings (true: enable; false: disable; nil: use last/default setting)

[MarekkPie]

The problem is...Lua makes nil return false.

Example:

Tnzu6.png (25.09 KiB) Viewed 270 times

[Xgoff]

The problem is...Lua makes nil return false.

Example:

my post probably wasn't very clear on it but you would test for true/false/nil explicitly (or at least the latter two) if you needed the distinction

[MarekkPie]

Interesting. Just tested and it worked.

[bartbes]

Actually, not nil is true, so it never reaches the third option, re-ordering them should do the trick.

[MarekkPie]

Actually, not nil is true, so it never reaches the third option, re-ordering them should do the trick.

Yup, that did it. Now you got the best of both worlds: succinct code and ternary testing.

Code: Select all

function nilTest(a)
	if a then
		print("true")
	elseif a == nil then
		print("nil")
	elseif not a then
		print("false")
	end
end

[Robin]

The below is equivalent:

Code: Select all

function nilTest(a)
	if a then
		print("true")
	elseif a == nil then
		print("nil")
	else
		print("false")
	end
end

If you can see why, you've got the hang of booleans.

[MarekkPie]

I just wanted to be verbose.

[kikito]

Well, succinct is pretty much the contrary of verbose, isn't it?

Little known fact: "nil and true" returns nil, not false. "false and true" returns false. "<Everything else> and true" returns true. With that knowledge, you an do this:

Code: Select all

function nilTest(a)
   print(a and true)
end

[MarekkPie]

I get the "false and true" because of short-circuiting. But that's interesting about nil and true. And makes it even more succinct (or is it verbose? Maybe succbose? )