LÖVE

winded wrote:Hi everyone!

So first a disclaimer - I'm super new to coding. Lua is the first language I've ever tried to learn. However, a lot of the tutorials and posts that you guys have on the forum have been super helpful - especially the ones from Kikito.

winded wrote:I just recently finished *almost* all of the lua_missions that he has up in Github, and I have a few questions about them:

1. I don't know any regular expressions, so I skipped the second half of patterns.lua. Is there a good place to learn them? Do I need to know them right away, or should I just wait and learn them if I need? What are they used for?

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winded wrote:2. I'm really thrown by metatables. In particular, I don't understand why in lines 66 and 75 of indices.lua, t2.x returns nil. It was just set to equal 1. That makes it seem like tables that have been associated with metatables can't be directly altered. Is that only the case when you're using the __newindex metamethod? Why?

winded wrote:3. I'm completely lost on exercise.lua. First, I don't understand why we're trying to use a metamethod on strings instead of tables, when the previous lesson was all about using them on tables. Do they work on strings? How do you set them up to work with strings? Second, it seems like you should be able to solve this with a simple function. For the first set, why wouldn't you just use this sort of thing:

Code: Select all

local function starts_with(input_string, snippet)
  return input_string:sub(1, #snippet) == snippet
end

The ends_with function would be really similar, just using #input_string to count backwards. These don't actually work, so I assume I'm approaching it wrong, since the hint is to use a metatable.

winded wrote:Again, I'm sorry if these questions are silly. I'm learning a TON, but I'm clearly still very much a beginner.

Thanks!

But I'd advise to still try to learn them, as they're very handy.

In that mission, Kikito is trying to show you that the __newindex function is saying that trying to set something on t2 will instead put it on t1.

local t2 = setmetatable({}, {
  __newindex = function(t, key, value)
    t1[key] = value * 10
  end
})
t2.x = 1

t1[key] = value * 10
t2[key] = value

Though, I agree with you that the simple function is the better way to go.

winded wrote:Thanks so much Inny! This was very helpful.

Code: Select all

local t2 = setmetatable({}, {
  __newindex = function(t, key, value)
    t1[key] = value * 10
  end
})
t2.x = 1

So it sounds like what you're saying is that since we're using __newindex, you'd have to define that metamethod as having both:

Code: Select all

t1[key] = value * 10
t2[key] = value

because otherwise it'll only be set in t1. Is that correct? It just seems strange to me because I don't think most other metamethods are like that, right?

setmetatable(t1, { __newindex = function () end })
setmetatable(t2, { __newindex = function (t, k, v)
    rawset(t, k, v) -- rawset so we don't get back into this metamethod
  end } )