Warning

The Warning module contains a single method named warn, and the module extends itself, making #warn available. #warn is called for all warnings issued by Ruby. By default, warnings are printed to $stderr.

Changing the behavior of #warn is useful to customize how warnings are handled by Ruby, for instance by filtering some warnings, and/or outputting warnings somewhere other than $stderr.

If you want to change the behavior of #warn you should use +Warning.extend(MyNewModuleWithWarnMethod)+ and you can use `super` to get the default behavior of printing the warning to $stderr.

Example:

module MyWarningFilter
  def warn(message, category: nil, **kwargs)
    if /some warning I want to ignore/.matches?(message)
      # ignore
    else
      super
    end
  end
end
Warning.extend MyWarningFilter

You should never redefine #warn (the instance method), as that will then no longer provide a way to use the default behavior.

The warning gem provides convenient ways to customize #warn.

Public Class Methods

Warning[category] → true or false click to toggle source

Returns the flag to show the warning messages for category. Supported categories are:

:deprecated: deprecation warnings

assignment of non-nil value to $, and $;
keyword arguments
proc/lambda without block

etc.

:experimental: experimental features

Pattern matching

 
               static VALUE
rb_warning_s_aref(VALUE mod, VALUE category)
{
    rb_warning_category_t cat = rb_warning_category_from_name(category);
    if (rb_warning_category_enabled_p(cat))
        return Qtrue;
    return Qfalse;
}

Warning[category] = flag → flag click to toggle source

Sets the warning flags for category. See ::[] for the categories.

 
               static VALUE
rb_warning_s_aset(VALUE mod, VALUE category, VALUE flag)
{
    unsigned int mask = rb_warning_category_mask(category);
    unsigned int disabled = warning_disabled_categories;
    if (!RTEST(flag))
        disabled |= mask;
    else
        disabled &= ~mask;
    warning_disabled_categories = disabled;
    return flag;
}

Public Instance Methods

warn(msg, category: nil) → nil click to toggle source

Writes warning message msg to $stderr. This method is called by Ruby for all emitted warnings. A category may be included with the warning.

See the documentation of the Warning module for how to customize this.

 
               static VALUE
rb_warning_s_warn(int argc, VALUE *argv, VALUE mod)
{
    VALUE str;
    VALUE opt;
    VALUE category = Qnil;

    rb_scan_args(argc, argv, "1:", &str, &opt);
    if (!NIL_P(opt)) rb_get_kwargs(opt, &id_category, 0, 1, &category);

    Check_Type(str, T_STRING);
    rb_must_asciicompat(str);
    if (!NIL_P(category)) {
        rb_warning_category_t cat = rb_warning_category_from_name(category);
        if (!rb_warning_category_enabled_p(cat)) return Qnil;
    }
    rb_write_error_str(str);
    return Qnil;
}