method

warn

v2_6_3 - Show latest stable - Class: Kernel

warn(*args, p2 = {})

public

If warnings have been disabled (for example with the -W0 flag), does nothing. Otherwise, converts each of the messages to strings, appends a newline character to the string if the string does not end in a newline, and calls Warning.warn with the string.

  warn("warning 1", "warning 2")

<em>produces:</em>

  warning 1
  warning 2

If the uplevel keyword argument is given, the string will be prepended with information for the given caller frame in the same format used by the rb_warn C function.

  # In baz.rb
  def foo
    warn("invalid call to foo", uplevel: 1)
  end

  def bar
    foo
  end

  bar

<em>produces:</em>

  baz.rb:6: warning: invalid call to foo

static VALUE
rb_warn_m(int argc, VALUE *argv, VALUE exc)
{
    VALUE opts, location = Qnil;

    if (!NIL_P(ruby_verbose) && argc > 0 &&
            (argc = rb_scan_args(argc, argv, "*:", NULL, &opts)) > 0) {
        VALUE str = argv[0], uplevel = Qnil;
        if (!NIL_P(opts)) {
            static ID kwds[1];
            if (!kwds[0]) {
                CONST_ID(kwds[0], "uplevel");
            }
            rb_get_kwargs(opts, kwds, 0, 1, &uplevel);
            if (uplevel == Qundef) {
                uplevel = Qnil;
            }
            else if (!NIL_P(uplevel)) {
                VALUE args[2];
                long lev = NUM2LONG(uplevel);
                if (lev < 0) {
                    rb_raise(rb_eArgError, "negative level (%ld)", lev);
                }
                args[0] = LONG2NUM(lev + 1);
                args[1] = INT2FIX(1);
                location = rb_vm_thread_backtrace_locations(2, args, GET_THREAD()->self);
                if (!NIL_P(location)) {
                    location = rb_ary_entry(location, 0);
                }
            }
        }
        if (argc > 1 || !NIL_P(uplevel) || !end_with_asciichar(str, '\n')) {
            VALUE path;
            if (NIL_P(uplevel)) {
                str = rb_str_tmp_new(0);
            }
            else if (NIL_P(location) ||
                     NIL_P(path = rb_funcall(location, rb_intern("path"), 0))) {
                str = rb_str_new_cstr("warning: ");
            }
            else {
                str = rb_sprintf("%s:%ld: warning: ",
                    rb_string_value_ptr(&path),
                    NUM2LONG(rb_funcall(location, rb_intern("lineno"), 0)));
            }
            RBASIC_SET_CLASS(str, rb_cWarningBuffer);
            rb_io_puts(argc, argv, str);
            RBASIC_SET_CLASS(str, rb_cString);
        }
        if (exc == rb_mWarning) {
            rb_must_asciicompat(str);
            rb_write_error_str(str);
        }
        else {
            rb_write_warning_str(str);
        }
    }
    return Qnil;
}

warn

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