Error: attempting to reference a deleted function

[himajin100000]

himajin100000 here!
> himajin100000 here!
> 
> I've updated my Visual Studio to version 16.0.0 Preview 4.3 and I am 
> encountering an error. I'm not good at C++. I hope someone helps me.
> 
> C:\PROGRA~2\MIB055~1\2019\Preview\VC\Tools\MSVC\14.20.27508\Include\list(1010): 
> error C2280: 'std::pair<_Kty,_Ty> &std::pair<_Kty,_Ty>::operator 
> =(volatile const std::pair<_Kty,_Ty> &)': attempting to reference a 
> deleted function

Though I dont't think I understood well, reading these posts
https://stackoverflow.com/questions/41794892/

and adding

WidgetDefinition() = default;
WidgetDefinition(const WidgetDefinition&) = delete;
WidgetDefinition& operator =(const WidgetDefinition&) = delete;

to WidgetDefinition class in WidgetDefinition.hxx seems to have done the 
trick.
(for inadequate understanding, I'm not submitting a patch. )