Maybe somekind offtop, but how to generally determine if variable is any class (and not primitive etc) before checking if it's instance of class?

[idchlife]

Thank you for this fantastic library!

[kikito]

Normally you would do this:

if x:isInstanceOf(MyClass) then ...

But of course this will fail if x is something like a number.

The nice thing is that isInstanceOf does not make assumptions about the first parameter you pass to it. You can use it this way:

if MyClass.isInstanceOf(x, MyClass) then ...

Notice that we're using . instead of : between MyClass and isInstanceOf. This is uglier than the previous example, but it will work, even if x is a number or nil. If you are doing this a lot, consider localizing the function:

local isInstanceOf = MyClass.isInstanceOf
...
if isInstanceOf(x, MyClass) then ...

Also, notice that you should not be using this a lot in the first place. Often you can replace these ifs by a call to a method, which returns true by default and false on instances of MyClass (for example).

[idchlife]

Thanks!

[idchlife]

@kikito unfortunately, it does not work :(

local class = require "middleclass"

local Product = class("Product")

local b = Product:new()
local c = 23

assert(Product.isInstanceOf(c, Product), "nope")

gives:

lua: /Users/igorandreev/.luarocks/share/lua/5.2/middleclass.lua:114: attempt to index local 'self' (a number value)
stack traceback:
    /Users/igorandreev/.luarocks/share/lua/5.2/middleclass.lua:114: in function 'isInstanceOf'
    tests/common.lua:8: in main chunk
    [C]: in ?

[kikito]

Ok. That might actually be a bug - apologies. I will try to give this a look during the weekend.

For now you should be able to "walk around the issue" by making sure that c is a table:

assert(type(c) == "table" and Product.isInstanceOf(c, Product), "nope")

What version of middleclass are you running? Line 114 should not be raising that error.

[idchlife]

@kikito middleclass 4.1-0 installed via luarocks

[kikito]

Hi there, I just pushed a change to master which should fix this issue. I have not released the a new version of middleclass because I want to fix a different issue first, so if you want it you'll have to download the middleclass.lua file from master. Apologies for the delay!

[idchlife]

@kikito no apologies needed! Thank you for this wonderful library and resolved issue!