LÖVE

Posted: **Tue May 26, 2020 11:34 pm**

When I create a table for a character, I can do it this way:

h01 = {}
h01.body = love.physics.newBody(runWorld, 350, 100, "dynamic")
h01.shape = love.physics.newRectangleShape(66, 92)
h01.fixture = love.physics.newFixture(h01.body, h01.shape, density)

Note h01.fixture are using previously defined properties as parameters for newFixture.

However, if I want to use metatable, it does not like "self":

Code: Select all

h01 = {}

function h01:Create()
    local this =
    {

        body = love.physics.newBody(runWorld, 350, 100, "dynamic"),
        shape = love.physics.newRectangleShape(66, 92),
        fixture = love.physics.newFixture(self.body, self.shape, density)


    }
    setmetatable(this, h01)
    return this
end

I got error:

Code: Select all


bad argument #1 to 'newFixture' (Body expected, got nil)

How should I refer to these 2 previously defined properties in fixture in this case?

Posted: **Tue May 26, 2020 11:52 pm**

At the point you're referencing body in the table, self doesn't yet have the meaning you want. You're probably going to have to do it the way you did in the first example. At least, that's what I've been doing.

Code: Select all

function h01:Create()
    local this =
    {

        body = love.physics.newBody(runWorld, 350, 100, "dynamic"),
        shape = love.physics.newRectangleShape(66, 92),

    }

    this.fixture = love.physics.newFixture(this.body, this.shape, density)

    setmetatable(this, h01)
    return this
end

Posted: **Wed May 27, 2020 12:18 am**

Code: Select all

function h01:Create()
    local tbl = {}
        tbl.body = love.physics.newBody(runWorld, 350, 100, "dynamic"),
        tbl.shape = love.physics.newRectangleShape(66, 92),
        tbl.fixture = love.physics.newFixture(tbl.body, tbl.shape, density)
    return setmetatable(tbl , h01)
end

"self" is just a hidden parameter passed to the function corresponding to the table calling the function.

Posted: **Wed May 27, 2020 12:47 am**

Thanks. I thought I could use "self" within the function when defining it.

Posted: **Wed May 27, 2020 1:11 am**

Consider the following for illustration purposes:

Code: Select all

local myTable = {}
function myTable.myFunc ( self ) -- note the use of ".", note that in a situation like this 'self' is just a convention
  print ( self == myTable )      -- prints true
end
-- is equivalent to
local myTable = {}
function myTable:myFunc ( ) -- note the use of ":", "self" is received implicitly
  print ( self == myTable ) -- prints true
end

-- these two are equivalent
myTable.myFunc(myTable)
myTable:myFunc()

When you use a colon (":") when calling a function contained within a table, the table itself is automatically passed to the function as its first parameter. And when you define a function inside a table using a colon, the table ("self") is received implicitly under the hood. It's all syntax sugar.

In your use case specifically, you were trying to use h01 itself as the "self", even though what you wanted to use was the newly created object (this, or tbl in zero's fix).

Posted: **Wed May 27, 2020 5:52 am**

Also in your code you tried to do some calculation on a field inside the same table declaration :

Code: Select all

-- error
local myTable = {
  a = 5,
  b = a * 2
}

You can't do that because a is not yet declared, if you want to do that:

Code: Select all

local myTable = {
  a = 5
}
myTable.b = myTable.a * 2
-- or
local myTable = {}
myTable.a = 5
myTable.b = myTable.a * 2

Posted: **Wed May 27, 2020 3:56 pm**

Thanks a lot. After played around for a while, I found out the way duaner mentioned works best for me.

LÖVE

How to use "self" properly?

How to use "self" properly?

Re: How to use "self" properly?

Re: How to use "self" properly?

Re: How to use "self" properly?

Re: How to use "self" properly?

Re: How to use "self" properly?

Re: How to use "self" properly?