inspect

static VALUE
sym_inspect(VALUE sym)
{
    VALUE str;
    ID id = SYM2ID(sym);
    rb_encoding *enc;
    const char *ptr;
    long len;
    char *dest;
    rb_encoding *resenc = rb_default_internal_encoding();

    if (resenc == NULL) resenc = rb_default_external_encoding();
    sym = rb_id2str(id);
    enc = STR_ENC_GET(sym);
    ptr = RSTRING_PTR(sym);
    len = RSTRING_LEN(sym);
    if ((resenc != enc && !rb_str_is_ascii_only_p(sym)) || len != (long)strlen(ptr) ||
        !rb_enc_symname_p(ptr, enc) || !sym_printable(ptr, ptr + len, enc)) {
        str = rb_str_inspect(sym);
        len = RSTRING_LEN(str);
        rb_str_resize(str, len + 1);
        dest = RSTRING_PTR(str);
        memmove(dest + 1, dest, len);
        dest[0] = ':';
    }
    else {
        char *dest;
        str = rb_enc_str_new(0, len + 1, enc);
        dest = RSTRING_PTR(str);
        dest[0] = ':';
        memcpy(dest + 1, ptr, len);
    }
    return str;
}