Attempt to index local 'self' (a nil value)

Question

I have a problem with classes. I got below error: Attempt to index local 'self' (a nil value) When I call the getter method of below class. Item.lua file: ``` require "classlib" Item = class("Item") function Item:__init() self.interval = 1 end function Item:getInterval() return self.interval end ``` I'm calling this getter function like this: ``` dofile("../src/item.lua") item = Item() function test_item() assert_equal(1, item.getInterval()) end ``` What's the problem here? Kind regards...

Accepted Answer

In general, you should call member functions by `:`.

In Lua, colon (`:`) represents a call of a function, supplying `self` as the first parameter.

Thus

```
A:foo()
```

Is roughly equal to

```
A.foo(A)
```

If you don't specify A as in `A.foo()`, the body of the function will try to reference `self` parameter, which hasn't been filled neither explicitly nor implicitly.

Note that if you call it from inside of the member function, `self` will be already available:

```
-- inside foo()
-- these two are analogous
self:bar()
self.bar(self)
```

All of this information you'll find in any good Lua book/tutorial.

Attempt to index local 'self' (a nil value)

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