1. Discriminated unions don't have any issues with strict aliasing, you are allowed to read a union member as long as it was the last union member being written

1. Discriminated unions don't have any issues with strict aliasing, you are allowed to read a union member as long as it was the last union member being written to, and the tag-member helps you identify that. 2. If you are trying to retrofit polymorphism in C maybe you are using the wrong tool for the job. 3. If you really want polymorphism you can create baseclass-struct with a void* this pointer and a bunch of function pointers as instance-functions. To "override" the struct you just instantiate it with different function pointers. If you want to inherit an existing struct you add a void* super-member into your this-data and instantiate it explicitly. For any function you don't want to override you use just call the existing function function and pass in you super-data as this. This is also safe as each subclass implementation only casts the void* this into itself which is a known struct of the same type as was last written to. You do have to split the data and keep super-class data in another struct one pointer-hop away but that shouldn't be a big issue.