Module: Warning

Defined in:

error.c,
error.c

Overview

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

Changing the behavior of Warning.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 Warning.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/.match?(message)
      # ignore
    else
      super
    end
  end
end
Warning.extend MyWarningFilter

You should never redefine Warning#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 Warning.warn.

Defined Under Namespace

Classes: buffer

Class Method Summary

• .[](category) ⇒ Boolean

  Returns the flag to show the warning messages for category.

• .[]=(category) ⇒ Object

  Sets the warning flags for category.

Instance Method Summary

• #warn(msg, category: nil) ⇒ nil

  Writes warning message msg to $stderr.

Class Method Details

.[](category) ⇒ Boolean

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

etc.

:experimental

experimental features

• Pattern matching

:performance

performance hints

• Shape variation limit

Returns:

• (Boolean)

# File 'error.c', line 225

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

.[]=(category) ⇒ Object

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

# File 'error.c', line 240

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;
}

Instance Method Details

#warn(msg, category: nil) ⇒ nil

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.

Returns:

• (nil)

# File 'error.c', line 264

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;
}