Encoding::Converter#replacement=

static VALUE
econv_set_replacement(VALUE self, VALUE arg)
{
    rb_econv_t *ec = check_econv(self);
    VALUE string = arg;
    int ret;
    rb_encoding *enc;

    StringValue(string);
    enc = rb_enc_get(string);

    ret = rb_econv_set_replacement(ec,
            (const unsigned char *)RSTRING_PTR(string),
            RSTRING_LEN(string),
            rb_enc_name(enc));

    if (ret == -1) {
        /* xxx: rb_eInvalidByteSequenceError? */
        rb_raise(rb_eUndefinedConversionError, "replacement character setup failed");
    }

    return arg;
}