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add tl-optional (#558)
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‎.agents/docs/2026-10-21-add-tl-optional-plan.md‎

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# Add tl::optional 1.1.0 as compat.tl-optional
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## Source and shape
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- Upstream: <https://github.com/TartanLlama/optional>.
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- Version: `1.1.0`, the newest stable tag observed with
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`git ls-remote --tags --refs`.
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- License: CC0-1.0.
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- Shape: Form B, header-only. The single public header is
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`include/tl/optional.hpp`; upstream's CMake INTERFACE target exposes
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`include/`. The package uses `include_dirs = { "*/include" }` and a trivial
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anchor C TU to provide a buildable `optional` lib target.
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- No features: the library has no optional compilable source component.
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Upstream's Catch2 tests are not part of the library.
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The header supports C++11/14/17. The package's own anchor is compiled as C++;
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consumers choose their language mode. The workspace test uses C++23, and a
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direct smoke test also compiles and runs the same API in C++14.
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## Download and mirror
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- GLOBAL:
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`https://github.com/TartanLlama/optional/archive/refs/tags/v1.1.0.tar.gz`
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- SHA-256:
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`88ece79f3de5ccaec4191951a222f95cc80c4381dafd3163bdb1ff87cedf3118`
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- The archive was downloaded twice and compared byte-for-byte; both copies had
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the same digest.
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- No verified `mcpp-res` release is available, so the descriptor uses the
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upstream plain-string URL fallback rather than inventing a CN mirror.
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## Automatic updates
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The package meets the automatic-update criteria: it has GitHub numeric tags,
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stable archive URLs, identical resources on all declared platforms, and future
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versions do not require a build-recipe change. `extensions.autoupdate` uses the
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prefixed `v${version}` tag spelling and the GitHub tag-archive URL template.
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## Test member
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`tests/examples/tl-optional/` is registered in the root workspace. It asserts:
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- value and empty construction, `value_or`, reset and emplace;
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- constexpr construction;
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- `map`, `and_then`, `or_else` and `map_or`;
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- reference optional binding, rebinding and mutation;
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- `take()` moving the value out and emptying the source;
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- `make_optional` preserving reference optionals.
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Every assertion affects the process exit status (`return ok ? 0 : 1`).
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## Verification
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Pending local validation and updater declaration checks.

‎mcpp.toml‎

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"tests/examples/websocket-features",
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"tests/examples/websocket-tls",
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"tests/examples/wolfssl",
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"tests/examples/tl-optional",
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"tests/examples/tray",
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"tests/examples/xsimd",
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"tests/examples/xxhash",

‎pkgs/c/compat.tl-optional.lua‎

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-- Form B inline descriptor for tl::optional — a single-header implementation
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-- of std::optional with monadic extensions and optional references.
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--
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-- HEADER-ONLY: upstream's CMake INTERFACE target exposes `include/`, and the
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-- only public header is `include/tl/optional.hpp`. Tests and packaging files
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-- stay outside the consumer's include path. A trivial anchor TU gives mcpp a
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-- buildable `optional` lib target, following compat.gtl / compat.safeint.
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--
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-- LANGUAGE FLOOR: upstream describes the library as C++11/14/17 and selects
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-- its monadic overloads with TL_OPTIONAL_CXX14. The package's own anchor is
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-- compiled as C++; consumers choose their language mode. The test uses the
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-- workspace default C++23 mode and directly compiles the same API in C++14.
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--
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-- No features: the library has one header and no optional compilable source.
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-- Its tests fetch Catch2 and are not part of the library.
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--
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-- No verified mcpp-res mirror is available, so the upstream URL is a plain
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-- string rather than a fabricated GLOBAL/CN resource table.
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package = {
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spec = "1",
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namespace = "compat",
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name = "tl-optional",
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description = "tl::optional — std::optional with monadic operations and reference support (header-only)",
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licenses = {"CC0-1.0"},
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repo = "https://github.com/TartanLlama/optional",
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type = "package",
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extensions = {
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autoupdate = {
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tag = "v${version}",
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url = "https://github.com/TartanLlama/optional/archive/refs/tags/${tag}.tar.gz",
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},
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},
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xpm = {
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linux = {
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["1.1.0"] = {
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url = "https://github.com/TartanLlama/optional/archive/refs/tags/v1.1.0.tar.gz",
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sha256 = "88ece79f3de5ccaec4191951a222f95cc80c4381dafd3163bdb1ff87cedf3118",
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},
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},
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macosx = {
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["1.1.0"] = {
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url = "https://github.com/TartanLlama/optional/archive/refs/tags/v1.1.0.tar.gz",
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sha256 = "88ece79f3de5ccaec4191951a222f95cc80c4381dafd3163bdb1ff87cedf3118",
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},
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},
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windows = {
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["1.1.0"] = {
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url = "https://github.com/TartanLlama/optional/archive/refs/tags/v1.1.0.tar.gz",
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sha256 = "88ece79f3de5ccaec4191951a222f95cc80c4381dafd3163bdb1ff87cedf3118",
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},
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},
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},
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mcpp = {
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language = "c++23",
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import_std = false,
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c_standard = "c11",
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include_dirs = { "*/include" },
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generated_files = {
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["mcpp_generated/tl_optional_anchor.c"] = [==[
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int mcpp_compat_tl_optional_headers_anchor(void) { return 0; }
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]==],
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},
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sources = { "mcpp_generated/tl_optional_anchor.c" },
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targets = { ["optional"] = { kind = "lib" } },
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deps = { },
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},
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}

‎tests/examples/tl-optional/mcpp.toml‎

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# tl-optional test project: exercise the standard optional surface plus the
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# extensions that distinguish this library from std::optional.
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[package]
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name = "tl-optional-tests"
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version = "0.1.0"
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[dependencies.compat]
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tl-optional = "1.1.0"

‎tests/examples/tl-optional/tests/optional.cpp‎

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// compat.tl-optional — assert value/empty state, observers, mutation, monadic
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// chaining, reference binding, and constexpr construction through the public
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// header. The test uses only the standard library in addition to tl/optional.
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#include <tl/optional.hpp>
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#include <cstdio>
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#include <string>
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#include <type_traits>
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int main() {
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bool ok = true;
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auto check = [&](bool condition, const char* what) {
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if (!condition) {
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std::printf("FAIL: %s\n", what);
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ok = false;
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}
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};
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tl::optional<int> value = tl::make_optional(42);
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tl::optional<int> empty = tl::nullopt;
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check(value.has_value() && *value == 42, "value construction and observer");
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check(!empty.has_value(), "nullopt constructs an empty optional");
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check(value.value_or(7) == 42 && empty.value_or(7) == 7,
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"value_or handles both states");
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constexpr tl::optional<int> constexpr_value = tl::make_optional(11);
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static_assert(constexpr_value.has_value(), "constexpr optional");
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value.reset();
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check(!value, "reset clears the value");
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value.emplace(21);
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check(value && *value == 21, "emplace constructs a new value");
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const auto doubled = empty.map([](int x) { return x * 2; });
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check(!doubled, "map on an empty optional stays empty");
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const auto mapped = tl::make_optional(21).map([](int x) { return x * 2; });
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check(mapped && *mapped == 42, "map transforms a present value");
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const auto chained = tl::make_optional(5).and_then([](int x) {
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return tl::make_optional(x * 3);
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});
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check(chained && *chained == 15, "and_then chains optional-producing calls");
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const auto fallback = empty.or_else([] { return tl::make_optional(13); });
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check(fallback && *fallback == 13, "or_else supplies a fallback");
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check(tl::make_optional(42).map_or([](int x) { return x + 1; }, 0) == 43,
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"map_or applies the mapper when present");
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check(empty.map_or([](int x) { return x + 1; }, 0) == 0,
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"map_or returns the fallback when empty");
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int first = 1;
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int second = 2;
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tl::optional<int&> reference = first;
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check(&*reference == &first, "reference optional binds the original object");
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reference = second;
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check(&*reference == &second, "assignment rebinds the reference");
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*reference = 9;
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check(second == 9, "writing through a reference optional mutates the object");
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tl::optional<std::string> text = std::string("hello");
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auto taken = text.take();
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check(taken && *taken == "hello" && !text,
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"take moves out the value and empties the source");
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static_assert(std::is_same<decltype(tl::make_optional<int&>(first)),
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tl::optional<int&>>::value,
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"make_optional preserves reference optionals");
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if (ok) {
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std::puts("tl-optional OK");
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}
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return ok ? 0 : 1;
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}

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