class Exception
Descendants of class Exception are used to
communicate between Kernel#raise
and rescue statements in begin ... end blocks. Exception objects carry information about the
exception – its type (the exception's class name), an optional
descriptive string, and optional traceback information. Exception subclasses may add additional
information like NameError#name.
Programs may make subclasses of Exception,
typically of StandardError or RuntimeError, 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 StandardError or RuntimeError 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 Exception are:
-
StandardError – default for
rescue -
fatal – impossible to rescue
In Files
- error.c
Parent
Public Class Methods
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.
Construct a new Exception object, optionally passing in a message.
static VALUE
exc_initialize(int argc, VALUE *argv, VALUE exc)
{
VALUE arg;
rb_scan_args(argc, argv, "01", &arg);
rb_iv_set(exc, "mesg", arg);
rb_iv_set(exc, "bt", Qnil);
return exc;
}
Public Instance Methods
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;
const ID id_mesg = idMesg;
if (exc == obj) return Qtrue;
if (rb_obj_class(exc) != rb_obj_class(obj)) {
int status = 0;
ID id_message, id_backtrace;
CONST_ID(id_message, "message");
CONST_ID(id_backtrace, "backtrace");
obj = rb_protect(try_convert_to_exception, obj, &status);
if (status || 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;
}
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)
{
ID bt;
VALUE obj;
CONST_ID(bt, "bt");
obj = rb_attr_get(exc, bt);
if (rb_backtrace_p(obj)) {
obj = rb_backtrace_to_str_ary(obj);
/* rb_iv_set(exc, "bt", obj); */
}
return obj;
}
Returns any backtrace associated with the exception. This method is similar to #backtrace, but the backtrace is an array of
Thread::Backtrace::Location.
Now, this method is not affected by #set_backtrace.
static VALUE
exc_backtrace_locations(VALUE exc)
{
ID bt_locations;
VALUE obj;
CONST_ID(bt_locations, "bt_locations");
obj = rb_attr_get(exc, bt_locations);
if (!NIL_P(obj)) {
obj = rb_backtrace_to_location_ary(obj);
}
return obj;
}
Returns the previous exception ($!) at the time this exception was raised. This is useful for wrapping exceptions and retaining the original exception information.
VALUE
exc_cause(VALUE exc)
{
ID id_cause;
CONST_ID(id_cause, "cause");
return rb_attr_get(exc, id_cause);
}
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;
}
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;
}
Returns the result of invoking exception.to_s. Normally this
returns the exception's message or name. By supplying a to_str method,
exceptions are agreeing to be used where Strings are expected.
static VALUE
exc_message(VALUE exc)
{
return rb_funcall(exc, rb_intern("to_s"), 0, 0);
}
Sets the backtrace information associated with exc. The
backtrace must be an array of String
objects or a single String in the format
described in #backtrace.
static VALUE
exc_set_backtrace(VALUE exc, VALUE bt)
{
return rb_iv_set(exc, "bt", rb_check_backtrace(bt));
}
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, rb_intern("mesg"));
if (NIL_P(mesg)) return rb_class_name(CLASS_OF(exc));
return rb_String(mesg);
}