c# - How could I put a constraint on a literal string parameter -

i have title poor able describe problem thing think of. anyway, suppose i've been given following enum:

public enum documenttype{       idcard=0,       passport,       driverslicense } 

and have method accepts string , returns above enum:

public documenttype getdoctypebystring(string doctype){     switch (doctype)     {        case "id":          return documenttype.idcard;        case "pass"          return documenttype.passport;        //and on     } } 

now, if passed string not meet of switch conditions? silliest thing make return type object, that's hardly ever it. if enum mine, add additional value called "none" , return in case of no match, have no control on it. thought, whether possible constrain input values. far c# concerned, totally sure it's not possible, decided ask anyway. would recommend in case?

no can't. pattern used throw a

throw new argumentexception("doctype"); 

technically

throw new argumentoutofrangeexception("doctype"); 

would correct, haven't ever seen used outside "numeric" indexes.

for example, enum.parse throw argumentexception if use illegal values, , method seems similar that.

other option use enum.tryparse pattern:

public static bool trygetdoctypebystring(string doctype, out documenttype documenttype)  {     switch (doctype)     {         case "id":             documenttype = documenttype.idcard;             return true;         case "pass"             documenttype = documenttype.passport;             return true;     }      documenttype = default(documenttype);     return false; }