c++ - Why throw a class over an enum? -

just wondering, why better throw class on enum

surely throwing classes more overhead?

e.g.

enum myexception {    except_a,    except_b,    except_c }   void function f(){   throw a; }   int main(int arc, char* argv[]){    try{    } catch (myexception e){     switch(e){       except_a: break;       except_b: break;       except_c: break;     }   }    return 0; } 

apart overhead. need declare class each 1 might override std::exception or something. more code, larger binary... what's benefit?

given

enum myexception {    except_a,    except_b,    except_c } 

write catch clause catches except_c exceptions.

with

struct my_except {}; struct my_except_a : my_except {}; struct my_except_b : my_except {}; struct my_except_c : my_except {}; 

that's easy, since can catch base class or derived classes.

many of common advantages of derivation apply exceptions. example, base classed can stand in derived classes , code needs know base classes deal derived exceptions. that's form of polymorphism, while enum switch on type.

the general rule polymorphism applies here, too: whenever tempted use switch on type, dismissing advantages of polymorphism. problems getting seen once code has expanded hundreds of kloc, , need add new type. polymorphism, that's easy, because code fine dealing base class references only.
type enum, have hunt down every single switch statement on enum , check whether need adapt it.

things these have killed more 1 company.

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here's afterthought: when they've done while, users start add kinds of data exception types. classic take __file__ , __line__ in exception's constructor able see exception came from. this, too, needs exceptions class types.