feat(solutions+ci): add reference solutions and dslings build CI for cpp11

.github/workflows/dslings-ref-ci.yml

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+name: Validate dslings reference solutions
+
+on:
+  push:
+    branches: ["main"]
+    paths:
+      - "dslings/**"
+      - "solutions/**"
+      - "d2x/**"
+      - "xmake.lua"
+      - ".github/workflows/dslings-ref-ci.yml"
+  pull_request:
+    paths:
+      - "dslings/**"
+      - "solutions/**"
+      - "d2x/**"
+      - "xmake.lua"
+      - ".github/workflows/dslings-ref-ci.yml"
+  workflow_dispatch:
+
+jobs:
+  build-and-run-reference:
+    runs-on: ubuntu-latest
+
+    env:
+      XLINGS_VERSION: "0.4.3"
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install Xlings ${{ env.XLINGS_VERSION }}
+        run: |
+          set -eu
+          curl -fsSL "https://github.com/d2learn/xlings/releases/download/v${XLINGS_VERSION}/xlings-${XLINGS_VERSION}-linux-x86_64.tar.gz" \
+            | tar -xzf - -C /tmp
+          /tmp/xlings-${XLINGS_VERSION}-linux-x86_64/bin/xlings self install
+          echo "$HOME/.xlings/subos/current/bin" >> "$GITHUB_PATH"
+
+      - name: Install xmake (via xlings)
+        run: xlings install xmake -y
+
+      - name: xmake config
+        run: xmake f -y
+
+      # Following steps go through the SAME `xmake d2x-buildtools` plugin
+      # path that `d2x checker` uses internally (see d2x/buildtools/xmake/main.lua).
+      # This way the CI exercises the real d2x integration code path, not a
+      # parallel xmake-only path. A passing CI here is what a learner would
+      # see if they ran `d2x checker cpp11-XX-feat-K-ref` locally.
+
+      - name: List all *-ref targets via d2x-buildtools
+        id: list_ref
+        run: |
+          set -eu
+          REF_TARGETS=$(xmake d2x-buildtools --command=list 2>/dev/null \
+            | tr ' ' '\n' \
+            | sed 's/@.*$//' \
+            | grep -E '\-ref$' \
+            | sort -u)
+          echo "Found $(echo "$REF_TARGETS" | wc -l) reference targets:"
+          echo "$REF_TARGETS"
+          echo "targets<<EOF" >> "$GITHUB_OUTPUT"
+          echo "$REF_TARGETS" >> "$GITHUB_OUTPUT"
+          echo "EOF" >> "$GITHUB_OUTPUT"
+
+      - name: Build all *-ref targets via d2x-buildtools
+        run: |
+          set -eu
+          while IFS= read -r tgt; do
+            [ -z "$tgt" ] && continue
+            echo "::group::build $tgt"
+            xmake d2x-buildtools --command=build --target="$tgt"
+            echo "::endgroup::"
+          done <<< "${{ steps.list_ref.outputs.targets }}"
+
+      - name: Run all *-ref targets via d2x-buildtools and assert no ❌
+        run: |
+          set -eu
+          fail=0
+          while IFS= read -r tgt; do
+            [ -z "$tgt" ] && continue
+            echo "::group::run $tgt"
+            output=$(xmake d2x-buildtools --command=run --target="$tgt" 2>&1)
+            echo "$output"
+            if echo "$output" | grep -qE '❌|Compilation/Running failed'; then
+              echo "::error::reference target $tgt produced a ❌ — exercise solution does not pass its own asserts"
+              fail=1
+            fi
+            if echo "$output" | grep -q 'Delete the D2X_WAIT to continue'; then
+              echo "::error::reference target $tgt still contains D2X_WAIT — remove it from the solution"
+              fail=1
+            fi
+            echo "::endgroup::"
+          done <<< "${{ steps.list_ref.outputs.targets }}"
+          exit $fail
+
+      - name: Verify dslings ↔ solutions filename parity
+        run: |
+          set -eu
+          # Every dslings/{cpp,hpp} file should have a matching solutions/ counterpart
+          missing=0
+          while IFS= read -r f; do
+            rel="${f#dslings/}"
+            # Skip the en/ mirror — solutions are language-neutral
+            case "$rel" in
+              en/*) continue ;;
+            esac
+            if [ ! -f "solutions/$rel" ]; then
+              echo "::warning::missing solutions/$rel (paired with dslings/$rel)"
+              missing=$((missing+1))
+            fi
+          done < <(find dslings -name '*.cpp' -not -path 'dslings/en/*')
+          if [ "$missing" -gt 0 ]; then
+            echo "::warning::$missing dslings exercises do not yet have a reference solution. This is informational during the bring-up phase; tighten to error once cpp11 is fully covered."
+          fi

solutions/cpp11/00-auto-and-decltype-0.cpp

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+// d2mcpp: https://github.com/mcpp-community/d2mcpp
+// license: Apache-2.0
+// reference solution for: dslings/cpp11/00-auto-and-decltype-0.cpp
+//
+// 用途: 仅给 CI 与维护者参考使用，不是教程入口。
+// 教程练习入口: dslings/cpp11/00-auto-and-decltype-0.cpp
+//
+
+#include <d2x/cpp/common.hpp>
+
+int main() {
+
+    // 0. 声明定义
+    int a = 1;
+    auto a1 = a;          // a1: int
+    int b = 2;
+    auto b1 = b;          // b1: int
+
+    decltype(b) b2 = b;   // b2: int
+    decltype(a) a2 = a;   // a2: int
+
+    char c = 'c';
+    auto c1 = c;          // c1: char
+    decltype(c) c2 = c;   // c2: char
+    (void)c1; (void)c2;
+
+    d2x_assert_eq(a, a1);
+    d2x_assert_eq(a1, a2);
+    d2x_assert_eq(b, b1);
+    d2x_assert_eq(b1, b2);
+
+    return 0;
+}

solutions/cpp11/00-auto-and-decltype-1.cpp

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+// d2mcpp: https://github.com/mcpp-community/d2mcpp
+// license: Apache-2.0
+// reference solution for: dslings/cpp11/00-auto-and-decltype-1.cpp
+//
+// 用途: 仅给 CI 与维护者参考使用，不是教程入口。
+// 教程练习入口: dslings/cpp11/00-auto-and-decltype-1.cpp
+//
+
+#include <d2x/cpp/common.hpp>
+
+int main() {
+
+    // 1. 表达式
+    int a = 1;
+    auto a1 = a + 2;
+    auto a2 = a + 2 + 1.1;       // double
+
+    int b = 2;
+    decltype(a + 0.1) b1 = a + 0.1; // double
+    decltype(a + b + 1.1) b2 = a + b + 1.1;
+    (void)a1; (void)b2;
+
+    char c = 'c';
+    auto c1 = 1 + c;             // int
+    decltype(2 + 'a') c2 = 2 + 'a';
+
+    d2x_assert_eq(a2, a + 2 + 1.1);
+    d2x_assert_eq(b1, a + 0.1);
+    d2x_assert_eq(c1, 1 + c);
+    d2x_assert_eq(c2, 2 + 'a');
+
+    return 0;
+}

solutions/cpp11/00-auto-and-decltype-2.cpp

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+// d2mcpp: https://github.com/mcpp-community/d2mcpp
+// license: Apache-2.0
+// reference solution for: dslings/cpp11/00-auto-and-decltype-2.cpp
+//
+// 用途: 仅给 CI 与维护者参考使用，不是教程入口。
+// 教程练习入口: dslings/cpp11/00-auto-and-decltype-2.cpp
+//
+
+#include <d2x/cpp/common.hpp>
+
+#include <iostream>
+#include <vector>
+#include <functional>
+
+int add_func(int a, int b) {
+    return a + b;
+}
+
+int main() {
+
+    // 2. 复杂类型
+
+    std::vector<int> v = {1, 2, 3};
+
+    std::vector<int>::iterator v1 = v.begin();
+    for (; v1 != v.end(); ++v1) {
+        std::cout << *v1 << " ";
+    }
+    std::cout << std::endl;
+
+    auto v2 = v.begin();
+    for (; v2 != v.end(); ++v2) {
+        std::cout << *v2 << " ";
+    }
+    std::cout << std::endl;
+
+    auto minus_func = [](int a, int b) { return a - b; };
+
+    std::vector<std::function<int(int, int)>> funcVec = {
+        add_func,
+        minus_func
+    };
+
+    d2x_assert_eq(funcVec[0](1, 2), 3);
+    d2x_assert_eq(funcVec[1](1, 2), -1);
+
+    return 0;
+}

solutions/cpp11/00-auto-and-decltype-3.cpp

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+// d2mcpp: https://github.com/mcpp-community/d2mcpp
+// license: Apache-2.0
+// reference solution for: dslings/cpp11/00-auto-and-decltype-3.cpp
+//
+// 用途: 仅给 CI 与维护者参考使用，不是教程入口。
+// 教程练习入口: dslings/cpp11/00-auto-and-decltype-3.cpp
+//
+
+#include <d2x/cpp/common.hpp>
+
+#include <iostream>
+#include <vector>
+
+// 3. 函数返回值类型
+
+auto add_func(int a, double b) -> decltype(a + b) {
+    return a + b;
+}
+
+template<typename T1, typename T2>
+auto minus_func(T1 a, T2 b) -> decltype(a - b) {
+    return a - b;
+}
+
+int main() {
+
+    d2x_assert_eq(minus_func(1, 2), -1);
+    d2x_assert_eq(minus_func(2, 1), 1);
+    d2x_assert_eq(minus_func(1, 2.1), -1.1);
+
+    return 0;
+}

solutions/cpp11/00-auto-and-decltype-4.cpp

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+// d2mcpp: https://github.com/mcpp-community/d2mcpp
+// license: Apache-2.0
+// reference solution for: dslings/cpp11/00-auto-and-decltype-4.cpp
+//
+// 用途: 仅给 CI 与维护者参考使用，不是教程入口。
+// 教程练习入口: dslings/cpp11/00-auto-and-decltype-4.cpp
+//
+
+#include <d2x/cpp/common.hpp>
+
+#include <type_traits>
+
+
+// 4. 类/结构体成员类型推导
+
+struct Object {
+    const int a;
+    double b;
+    Object() : a(1), b(2.0) { }
+};
+
+int main() {
+    const Object obj;
+
+    bool type_check = false;
+
+    // obj的类型推导 和 (obj) 的类型推导
+    type_check = std::is_same<decltype(obj), const Object>::value;
+    d2x_assert(type_check); type_check = false; // dont change this line
+    type_check = std::is_same<decltype((obj)), const Object &>::value;
+    d2x_assert(type_check); type_check = false; // dont change this line
+
+    // obj.a的类型推导 和 (obj.a) 的类型推导
+    type_check = std::is_same<decltype(obj.a), const int>::value;
+    d2x_assert(type_check); type_check = false; // dont change this line
+    type_check = std::is_same<decltype((obj.a)), const int &>::value;
+    d2x_assert(type_check); type_check = false; // dont change this line
+
+    // obj.b的类型推导 和 (obj.b) 的类型推导
+    type_check = std::is_same<decltype(obj.b), double>::value;
+    d2x_assert(type_check); type_check = false; // dont change this line
+    type_check = std::is_same<decltype((obj.b)), const double &>::value;
+    d2x_assert(type_check); type_check = false; // dont change this line
+
+    return 0;
+}

solutions/cpp11/01-default-and-delete-0.cpp

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+// d2mcpp: https://github.com/mcpp-community/d2mcpp
+// license: Apache-2.0
+// reference solution for: dslings/cpp11/01-default-and-delete-0.cpp
+//
+// 用途: 仅给 CI 与维护者参考使用，不是教程入口。
+// 教程练习入口: dslings/cpp11/01-default-and-delete-0.cpp
+//
+
+#include <d2x/cpp/common.hpp>
+
+#include <iostream>
+
+// default和delete显式控制 -> 编译器默认构造函数的生成行为
+struct A { };
+struct B {
+    B() = default;
+    B(int x) { std::cout << "B(int x)" << std::endl; (void)x; }
+};
+struct C {
+    C() = default;
+    C(int x) { std::cout << "C(int x): " << x << std::endl; }
+};
+
+int main() { // 不要直接修改main函数中的代码
+
+    A a;
+    B b;
+    C c(1);
+    (void)a; (void)b; (void)c;
+
+    return 0;
+}

solutions/cpp11/01-default-and-delete-1.cpp

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+// d2mcpp: https://github.com/mcpp-community/d2mcpp
+// license: Apache-2.0
+// reference solution for: dslings/cpp11/01-default-and-delete-1.cpp
+//
+// 用途: 仅给 CI 与维护者参考使用，不是教程入口。
+// 教程练习入口: dslings/cpp11/01-default-and-delete-1.cpp
+//
+
+#include <d2x/cpp/common.hpp>
+
+#include <iostream>
+
+// 实现std::unique_ptr不可以拷贝, 但可以移动的属性
+struct UniquePtr {
+    void *dataPtr;
+    UniquePtr() = default;
+
+    UniquePtr(const UniquePtr&) = delete;
+    UniquePtr& operator=(const UniquePtr&) = delete;
+
+    UniquePtr(UniquePtr&&) = default;
+    UniquePtr& operator=(UniquePtr&&) = default;
+};
+
+int main() { // 不要直接修改main函数中的代码
+
+    UniquePtr a;
+
+    d2x_assert(std::is_copy_constructible<UniquePtr>::value == false);
+    d2x_assert(std::is_copy_assignable<UniquePtr>::value == false);
+    d2x_assert(std::is_move_constructible<UniquePtr>::value == true);
+    d2x_assert(std::is_move_assignable<UniquePtr>::value == true);
+    (void)a;
+
+    return 0;
+}