Extended maintenance of Ruby 1.9.3 ended on February 23, 2015. Read more

In Files

  • error.c

Exception

Descendants of class Exception are used to communicate between raise methods 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. Programs may subclass Exception, or more typically StandardError to provide custom classes and add additional information.

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 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

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;
    ID id_mesg;

    if (exc == obj) return Qtrue;
    CONST_ID(id_mesg, "mesg");

    if (rb_obj_class(exc) != rb_obj_class(obj)) {
        ID id_message, id_backtrace;
        CONST_ID(id_message, "message");
        CONST_ID(id_backtrace, "backtrace");

        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)
{
    ID bt;

    CONST_ID(bt, "bt");
    return rb_attr_get(exc, bt);
}
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;
}
inspect → string click to toggle source

Return this exception’s class name an 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. 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);
}
set_backtrace(array) → array click to toggle source

Sets the backtrace information associated with exc. The argument must be an array of String objects in the format described in Exception#backtrace.

 
               static VALUE
exc_set_backtrace(VALUE exc, VALUE bt)
{
    return rb_iv_set(exc, "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, rb_intern("mesg"));
    VALUE r = Qnil;

    if (NIL_P(mesg)) return rb_class_name(CLASS_OF(exc));
    r = rb_String(mesg);
    return r;
}