value equality check does not work as described

[mezzodrinker]

In the MobTalkerScript source code (namely the documentation of net.mobtalker.mobtalkerscript.v3.value.MtsValue.isEqual(MtsValue)), the description of the == (equals) operator states that two values are only equal if...

• ...their equals(Object) method returns true or...
• ...both objects' __eq meta methods are the same AND return true.

Currently, the check if the __eq meta methods are the same is redundant because it always yields false (as in, they always equal):

MtsValue tagA = getMetaTag( __eq );
if ( tagA.isNil() || !tagA.equals( getMetaTag( __eq ) ) )
    return false;

The error is located in line 402. It should be !tagA.equals( b.getMetaTag( __eq ) ) instead of !tagA.equals( getMetaTag( __eq ) ).

[mezzodrinker]

Tested with the following script:

MyClass = {}
function MyClass:new()
  local newInstance = {}
  setmetatable(newInstance, {
    __index = self,
    __eq = function(a, b)
      return true
    end
  })
  return newInstance
end

MyOtherClass = {}
function MyOtherClass:new()
  local newInstance = {}
  setmetatable(newInstance, {
    __index = self,
    __eq = function(a, b)
      return true
    end
  })
  return newInstance
end

instA = MyClass.new()
instB = MyOtherClass.new()

print(instA == instB)

This script will output true with the current implementation, but output false with line 402 changed.

[mezzodrinker]

Ensure __eq meta-methods of both values are compared (fixes #39)

→ <<cset d1e266314998>>

[mezzodrinker]

Reopening because the behaviour of the value equality check is not equal to how Lua handles it.

Code

C1 = {}
function C1:new()
  local inst = {}
  setmetatable(inst, {
    class = 'C1',
    __index = self,
    __eq = function (a,b)
      print('Hello from C1 __eq function')
      return true
    end
  })
  return inst
end

C2 = {}
function C2:new()
  local inst = {}
  setmetatable(inst, {
    class = 'C2',
    __index = self,
    __eq = function (a,b)
      print('Hello from C2 __eq function')
      return false
    end
  })
  return inst
end

equals = function (a,b)
  print('Hello from equals function')
  return true
end

C3 = {}
function C3:new()
  local inst = {}
  setmetatable(inst, {
    class = 'C3',
    __index = self,
    __eq = equals
  })
  return inst
end

C4 = {}
function C4:new()
  local inst = {}
  setmetatable(inst, {
    class = 'C4',
    __index = self,
    __eq = equals
  })
  return inst
end

-- Tests
inst1 = C1.new()
inst2 = C2.new()
inst3 = C3.new()
inst4 = C4.new()

print('inst1 == inst1? (expected true) ', inst1 == inst1)
print('inst2 == inst2? (expected true) ', inst2 == inst2)
print('inst3 == inst3? (expected true) ', inst3 == inst3)
print('inst4 == inst4? (expected true) ', inst4 == inst4)
print('inst1 == inst2? (expected true) ', inst1 == inst2)
print('inst2 == inst1? (expected false)', inst2 == inst1)
print('inst1 == inst3? (expected true) ', inst1 == inst3)
print('inst3 == inst1? (expected true) ', inst3 == inst1)
print('inst2 == inst3? (expected false)', inst2 == inst3)
print('inst3 == inst2? (expected true) ', inst3 == inst2)
print('inst3 == inst4? (expected true) ', inst3 == inst4)
print('inst4 == inst3? (expected true) ', inst4 == inst3)

Lua output

inst1 == inst1? (expected true)     true
inst2 == inst2? (expected true)     true
inst3 == inst3? (expected true)     true
inst4 == inst4? (expected true)     true
Hello from C1 __eq function
inst1 == inst2? (expected true)     true
Hello from C2 __eq function
inst2 == inst1? (expected false)    false
Hello from C1 __eq function
inst1 == inst3? (expected true)     true
Hello from equals function
inst3 == inst1? (expected true)     true
Hello from C2 __eq function
inst2 == inst3? (expected false)    false
Hello from equals function
inst3 == inst2? (expected true)     true
Hello from equals function
inst3 == inst4? (expected true)     true
Hello from equals function
inst4 == inst3? (expected true)     true

MTS 3.0.4 output

inst1 == inst1? (expected true) true
inst2 == inst2? (expected true) true
inst3 == inst3? (expected true) true
inst4 == inst4? (expected true) true
inst1 == inst2? (expected true) false
inst2 == inst1? (expected false)false
inst1 == inst3? (expected true) false
inst3 == inst1? (expected true) false
inst2 == inst3? (expected false)false
inst3 == inst2? (expected true) false
Hello from equals function
inst3 == inst4? (expected true) true
Hello from equals function
inst4 == inst3? (expected true) true

MTS 3.0.6 output

inst1 == inst1? (expected true) true
inst2 == inst2? (expected true) true
inst3 == inst3? (expected true) true
inst4 == inst4? (expected true) true
inst1 == inst2? (expected true) false
inst2 == inst1? (expected false)false
inst1 == inst3? (expected true) false
inst3 == inst1? (expected true) false
inst2 == inst3? (expected false)false
inst3 == inst2? (expected true) false
Hello from equals function
inst3 == inst4? (expected true) true
Hello from equals function
inst4 == inst3? (expected true) true

[mezzodrinker]

Fix #39

Reworked regression test for #39 (expected results based on Lua 5.3.3) Removed equality check for __eq meta-methods

→ <<cset e5c586c38851>>