Function FL_ABLE 

pub fn FL_ABLE(obj: VALUE) -> bool

Check if an object can have flags (akin to RB_FL_ABLE).

Returns false for immediate values (nil, true, false, Fixnum, Symbol, Flonum). Returns true for heap-allocated objects that can have flags set.

@param[in] obj An object to check. @retval true The object can have flags. @retval false The object is an immediate value.