一份Linq to object的C++实现几个月的构想+0.5小时的设计+4小时的linq.h编码+3小时的测试编码。 大量使用C++11的特性，在GCC 4.7.2下编译通过。
关于实现相关的描述就不说了，我表达能力差，恐怕讲清楚还需要好几个小时。具体使用参见测试码。 上代码： (1) linq.h  View Code
(2) 测试代码main.cpp （比我的代码更烂的是我的英语）  #include "pch.h" #include "linq.h" #include <vector> #include <string> #include <algorithm> template<typename T> void printC(const T& v) { for (auto i : v) cout << i << ','; cout << endl; } template<typename T> void print(const T& v) { cout << v << endl; } bool startsWith(const std::string& s, const std::string& prefix) { return s.find(prefix) == 0; } void featureTest() { // 1. standard { auto query = range(10) .where([](int i){ return i % 2; }) .select([](int i){ return i + 1; }); auto ref = {2, 4, 6, 8, 10}; assert(std::equal(ref.begin(), ref.end(), query.begin())); } // 2. deferred range { assert(range(123LL, 1000000000000LL).first() == 123); } // 3. deferred action { int selectCnt = 0; auto query = range(1, 1000) .where([](int i){ return i % 2 == 0; }) .select([&selectCnt](int i) { ++selectCnt; return i; }) .where([](int i) { return i % 4 == 0; }) .head(2); auto query2 = query; for (auto i : query) {} assert(selectCnt == 4); for (auto i : query2) {} assert(selectCnt == 8); } // 4. copy semantic { auto query = range(10).head(5); auto query2 = query; auto ref = {0, 1, 2, 3, 4}; assert(std::equal(ref.begin(), ref.end(), query.begin())); assert(std::equal(ref.begin(), ref.end(), query2.begin())); auto iter = query.begin(); ++iter; auto iter2 = iter; ref = {1, 2, 3, 4}; assert(std::equal(ref.begin(), ref.end(), iter)); assert(std::equal(ref.begin(), ref.end(), iter2)); } // 5. always reference the neweast data of dataSource { std::vector<std::string> dataSrc{"A_abc", "A_def", "B_abc", "B_def"}; auto query = from(dataSrc) .head(3) .where([](const std::string& s) { return startsWith(s, "B_"); }); auto ref = {"B_abc"}; assert(std::equal(ref.begin(), ref.end(), query.begin())); dataSrc.clear(); dataSrc.shrink_to_fit(); dataSrc = {"B#_abc", "B_123", "B_1234", "B_321", "B_111"}; ref = {"B_123", "B_1234"}; assert(std::equal(ref.begin(), ref.end(), query.begin())); } // 6. invoke the operator new as least as possible { } // 7. you can use query after the dataSource has been destroyed, by the use of 'reserve' { Enumerable<int> query; { std::vector<int> v{1, 2, 3, 4}; // query = from(v).select([](int i){ return i % 2; }); query = from(v).reserve().select([](int i){ return i % 2; }); auto ref = {1, 0, 1, 0}; assert(std::equal(ref.begin(), ref.end(), query.begin())); } auto ref = {1, 0, 1, 0}; assert(std::equal(ref.begin(), ref.end(), query.begin())); } // 8. add action to an exist query { auto query = range(10).where([](int i){ return i < 5;}); auto ref = {0, 1, 2, 3, 4}; assert(std::equal(ref.begin(), ref.end(), query.begin())); auto query2 = query.select([](int i){ return i * i; }); ref = {0, 1, 4, 9, 16}; assert(std::equal(ref.begin(), ref.end(), query2.begin())); } } void functionTest() { // 1. from, select, where, cast { int a[]{5, 6, 7, 8, 9}; auto query = from(a) .where([](int i){ return i % 3; }) .select([](int i) { return i * i;}); auto ref = {25, 49, 64}; assert(std::equal(ref.begin(), ref.end(), query.begin())); } // 2. range, all, any { assert(range(10).all([](int i){ return i >= 0;})); assert(!range(10).all([](int i){ return i > 0;})); assert(from(std::vector<std::string>{"_a", "b"}) .any([](const std::string& s){ return startsWith(s, "_"); })); assert(!from(std::vector<std::string>{"@a", "b"}) .any([](const std::string& s){ return startsWith(s, "_"); })); } // 3. cast, average { assert(range(1, 5).average() == 2); assert(range(1, 5).cast<float>().average() == 2.5); } // 4. contain, count { int a[]{1, 2, 1, 1, 3, 2, }; assert(from(a).contain(3)); assert(!from(a).contain(4)); assert(from(a).count(1) == 3); assert(from(a).count([](int i) { return i % 2; }) == 4); } // 5. first, last, head, tail { int a[]{3, 5, 7, 9, 11}; assert(from(a).first() == 3); assert(from(a).last() == 11); auto ref = {3, 5}; auto query = from(a).head(2); assert(std::equal(ref.begin(), ref.end(), query.begin())); ref = {7, 9, 11}; query = from(a).tail(3); assert(std::equal(ref.begin(), ref.end(), query.begin())); } // 6. groupBy { auto query = range(10).groupBy([](int i) { return i % 3;}); int refs[][4] = { {0, 3, 6, 9}, {1, 4, 7,}, {2, 5, 8,}, }; int n = 0; for (auto i : query) { assert(i.first == refs[n][0]); assert(std::equal(i.second.begin(), i.second.end(), refs[n])); ++n; } assert(n == 3); } // 7. takeUntil, skipUntil { auto query = range(10).takeUntil([](int i){ return i > 5; }); auto ref = {0, 1, 2, 3, 4, 5}; assert(std::equal(ref.begin(), ref.end(), query.begin())); query = range(10).skipUntil([](int i){ return i > 5; }); ref = { 6, 7, 8, 9}; assert(std::equal(ref.begin(), ref.end(), query.begin())); } // 8. max, min { int a[]{3, 2, 5, 8, 10, -3}; assert(from(a).min() == -3); assert(from(a).max() == 10); } // 9. reduce { assert(range(1, 11).reduce([](int a, int b){ return a + b; }) == 55); assert(range(1, 11).reduce([](int a, int b){ return a * b; }, 0) == 0); assert(range(1, 11).reduce([](int a, int b){ return a * b; }, 1) == 3628800); } // 10. unique, sort, random { int a[]{3, 5, 5, 4, 2, 1, 2}; auto query = from(a).unique(); auto ref = {3, 5, 4, 2, 1}; assert(std::equal(ref.begin(), ref.end(), query.begin())); ref = {5, 4, 3, 2, 1}; query = query.sort().sort([](int a, int b){ return a > b; }); assert(std::equal(ref.begin(), ref.end(), query.begin())); query = query.random(); assert(!std::equal(ref.begin(), ref.end(), query.begin())); } // 11. intersect, _union { int a[]{3, 5, 11}; auto query = range(10).intersect(from(a)); auto ref = {3, 5}; assert(std::equal(ref.begin(), ref.end(), query.begin())); ref = {3, 4, 5, 6}; query = query._union(range(4, 7)); assert(std::equal(ref.begin(), ref.end(), query.begin())); } } int main() { featureTest(); functionTest(); } 为什么不把它提交到git hub之类的专门代码仓库？一则我没有用过，二则，这种代码是我的write-only构想实践码，不提供后续维护的：） 评论列表
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