class() calls constructor of previously created class

[asb]

I recently updated from a a previous Penlight version to latest git head and have encountered a bug which breaks my code using class() from pl.class. Hopefully this example demonstrates the problem - I don't believe there's any reason for A's constructor to be called when defining class B.

$ cat t.lua
class = require("pl.class").class

A = class()
function A:_init(mandatory)
  assert(mandatory, "tried to initialise instance with no arg")
end
B = class()

$ lua t.lua
lua: t.lua:5: tried to initialise instance with no arg
stack traceback:
  [C]: in function 'assert'
  t.lua:5: in function '_init'
  ./pl/class.lua:18: in function 'call_ctor'
  ./pl/class.lua:84: in function 'class'
  t.lua:7: in main chunk
  [C]: ?

[stevedonovan]

Yeah, I see exactly what you mean - it's a sneaky feature. It allows a certain lazy style of inheritance; base ctor takes a string; subclasses can be made without explicit ctors, confident that the base ctor will be passed the string. Well, if you remember to pass it, of course - nasty stuff to document! I am tending towards 'everything is explicit' these days so maybe it should just go.

[asb]

But A:_init is an instance constructor - why would it ever be correct that it would be called when creating a new class? Have I not 1) created a new class and assigned it to A. 2) defined _init for class A and 3) created a new class and assigned it to B? Why should action 3) results in A:_init being called?

[stevedonovan]

Sorry, I misread you - I tried exactly the code you gave, and yes, I get also get a ridiculous result! Genuine, first class bug!

[stevedonovan]

This is very interesting - pl.class is one of the modules that changed - require 'pl.class' returns the actual class object. So if were

    class = require ('pl.class')

then things work fine - which is why I didn't see the problem at first. By some horrible fluke class.class exists and is a function, so everything looks hunky dory until it falls over.

[asb]

Ah I see, the previous version of Penlight I was using exported something like class, Map, and Set. But as you say it just returns pl.class now, so when I do require("pl.class").class the __index on the returned pl.class is called. This is a case of programmer error resulting from API breakage that probably turned out to cause more trouble than intended (due to the __index on pl.class). I'll mark it closed.

[stevedonovan]

What I will do is detect this particular case and issue a stern warning, otherwise it is going to cause confusion! (The other option is to regard it as an error)