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    Exception

    Descendants of class are used to communicate between and rescue statements in begin ... end blocks. objects carry information about the exception - its type (the exception's class name), an optional descriptive string, and optional traceback information. subclasses may add additional information like .

    Programs may make subclasses of , typically of or , to provide custom classes and add additional information. See the subclass list below for defaults for raise and rescue.

    When an exception has been raised but not yet handled (in rescue, ensure, at_exit and END blocks) the global variable $! will contain the current exception and $@ contains the current exception's backtrace.

    It is recommended that a library should have one subclass of or and have specific exception types inherit from it. This allows the user to rescue a generic exception type to catch all exceptions the library may raise even if future versions of the library add new exception subclasses.

    For example: 

    class MyLibrary
 class Error < RuntimeError
 end
 class WidgetError < Error
 end
 class FrobError < Error
 end
end

    To handle both WidgetError and FrobError the library user can rescue MyLibrary::Error.

    The built-in subclasses of are:

    Public Class Methods

    exception(string) → an_exception or exc click to toggle source

    With no argument, or if the argument is the same as the receiver, return the receiver. Otherwise, create a new exception object of the same class as the receiver, but with a message equal to string.to_str.

    new(msg = nil) → exception click to toggle source

    Construct a new object, optionally passing in a message. 

     static VALUE
exc_initialize(int argc, VALUE *argv, VALUE exc)
{
 VALUE arg;
 arg = (!rb_check_arity(argc, 0, 1) ? Qnil : argv[0]);
 return exc_init(exc, arg);
}
    to_tty? → true or false click to toggle source

    Returns true if exception messages will be sent to a tty. 

     static VALUE
exc_s_to_tty_p(VALUE self)
{
 return rb_stderr_tty_p() ? Qtrue : Qfalse;
}

    Public Instance Methods

    exc == obj → true or false click to toggle source

    Equality-If obj is not an Exception, returns false. Otherwise, returns true if exc and obj share same class, messages, and backtrace. 

     static VALUE
exc_equal(VALUE exc, VALUE obj)
{
 VALUE mesg, backtrace;
 if (exc == obj) return Qtrue;
 if (rb_obj_class(exc) != rb_obj_class(obj)) {
 int state;
 obj = rb_protect(try_convert_to_exception, obj, &state);
 if (state || obj == Qundef) {
 rb_set_errinfo(Qnil);
 return Qfalse;
 }
 if (rb_obj_class(exc) != rb_obj_class(obj)) return Qfalse;
 mesg = rb_check_funcall(obj, id_message, 0, 0);
 if (mesg == Qundef) return Qfalse;
 backtrace = rb_check_funcall(obj, id_backtrace, 0, 0);
 if (backtrace == Qundef) return Qfalse;
 }
 else {
 mesg = rb_attr_get(obj, id_mesg);
 backtrace = exc_backtrace(obj);
 }
 if (!rb_equal(rb_attr_get(exc, id_mesg), mesg))
 return Qfalse;
 if (!rb_equal(exc_backtrace(exc), backtrace))
 return Qfalse;
 return Qtrue;
}
    backtrace → array click to toggle source

    Returns any backtrace associated with the exception. The backtrace is an array of strings, each containing either "filename:lineNo: in `method''' or "filename:lineNo.'' 

    def a
 raise "boom"
end
def b
 a()
end
begin
 b()
rescue => detail
 print detail.backtrace.join("\n")
end

    produces: 

    prog.rb:2:in `a'
prog.rb:6:in `b'
prog.rb:10
     static VALUE
exc_backtrace(VALUE exc)
{
 VALUE obj;
 obj = rb_attr_get(exc, id_bt);
 if (rb_backtrace_p(obj)) {
 obj = rb_backtrace_to_str_ary(obj);
 /* rb_ivar_set(exc, id_bt, obj); */
 }
 return obj;
}
    backtrace_locations → array click to toggle source

    Returns any backtrace associated with the exception. This method is similar to , but the backtrace is an array of .

    Now, this method is not affected by . 

     static VALUE
exc_backtrace_locations(VALUE exc)
{
 VALUE obj;
 obj = rb_attr_get(exc, id_bt_locations);
 if (!NIL_P(obj)) {
 obj = rb_backtrace_to_location_ary(obj);
 }
 return obj;
}
    cause → an_exception or nil click to toggle source

    Returns the previous exception ($!) at the time this exception was raised. This is useful for wrapping exceptions and retaining the original exception information. 

     static VALUE
exc_cause(VALUE exc)
{
 return rb_attr_get(exc, id_cause);
}
    exception(string) → an_exception or exc click to toggle source

    With no argument, or if the argument is the same as the receiver, return the receiver. Otherwise, create a new exception object of the same class as the receiver, but with a message equal to string.to_str. 

     static VALUE
exc_exception(int argc, VALUE *argv, VALUE self)
{
 VALUE exc;
 if (argc == 0) return self;
 if (argc == 1 && self == argv[0]) return self;
 exc = rb_obj_clone(self);
 exc_initialize(argc, argv, exc);
 return exc;
}
    full_message(highlight: bool, order: [:top or :bottom]) → string click to toggle source

    Returns formatted string of exception. The returned string is formatted using the same format that Ruby uses when printing an uncaught exceptions to stderr.

    If highlight is true the default error handler will send the messages to a tty.

    order must be either of :top or :bottom, and places the error message and the innermost backtrace come at the top or the bottom.

    The default values of these options depend on $stderr and its tty? at the timing of a call. 

     static VALUE
exc_full_message(int argc, VALUE *argv, VALUE exc)
{
 VALUE opt, str, emesg, errat;
 enum {kw_highlight, kw_order, kw_max_};
 static ID kw[kw_max_];
 VALUE args[kw_max_] = {Qnil, Qnil};
 rb_scan_args(argc, argv, "0:", &opt);
 if (!NIL_P(opt)) {
 if (!kw[0]) {
#define INIT_KW(n) kw[kw_##n] = rb_intern_const(#n)
 INIT_KW(highlight);
 INIT_KW(order);
#undef INIT_KW
 }
 rb_get_kwargs(opt, kw, 0, kw_max_, args);
 switch (args[kw_highlight]) {
 default:
 rb_raise(rb_eArgError, "expected true or false as "
 "highlight: %+"PRIsVALUE, args[kw_highlight]);
 case Qundef: args[kw_highlight] = Qnil; break;
 case Qtrue: case Qfalse: case Qnil: break;
 }
 if (args[kw_order] == Qundef) {
 args[kw_order] = Qnil;
 }
 else {
 ID id = rb_check_id(&args[kw_order]);
 if (id == id_bottom) args[kw_order] = Qtrue;
 else if (id == id_top) args[kw_order] = Qfalse;
 else {
 rb_raise(rb_eArgError, "expected :top or :bottom as "
 "order: %+"PRIsVALUE, args[kw_order]);
 }
 }
 }
 str = rb_str_new2("");
 errat = rb_get_backtrace(exc);
 emesg = rb_get_message(exc);
 rb_error_write(exc, emesg, errat, str, args[kw_highlight], args[kw_order]);
 return str;
}
    inspect → string click to toggle source

    Return this exception's class name and message. 

     static VALUE
exc_inspect(VALUE exc)
{
 VALUE str, klass;
 klass = CLASS_OF(exc);
 exc = rb_obj_as_string(exc);
 if (RSTRING_LEN(exc) == 0) {
 return rb_str_dup(rb_class_name(klass));
 }
 str = rb_str_buf_new2("#<");
 klass = rb_class_name(klass);
 rb_str_buf_append(str, klass);
 rb_str_buf_cat(str, ": ", 2);
 rb_str_buf_append(str, exc);
 rb_str_buf_cat(str, ">", 1);
 return str;
}
    message → string click to toggle source

    Returns the result of invoking exception.to_s. Normally this returns the exception's message or name. 

     static VALUE
exc_message(VALUE exc)
{
 return rb_funcallv(exc, idTo_s, 0, 0);
}
    set_backtrace(backtrace) → array click to toggle source

    Sets the backtrace information associated with exc. The backtrace must be an array of objects or a single in the format described in . 

     static VALUE
exc_set_backtrace(VALUE exc, VALUE bt)
{
 return rb_ivar_set(exc, id_bt, rb_check_backtrace(bt));
}
    to_s → string click to toggle source

    Returns exception's message (or the name of the exception if no message is set). 

     static VALUE
exc_to_s(VALUE exc)
{
 VALUE mesg = rb_attr_get(exc, idMesg);
 if (NIL_P(mesg)) return rb_class_name(CLASS_OF(exc));
 return rb_String(mesg);
}

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