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
![[C++]一份Linq to object的C++实现](https://johngo-pic.oss-cn-beijing.aliyuncs.com/articles/20230526/ContractedBlock.gif)
![[C++]一份Linq to object的C++实现](https://www.johngo689.com/wp-content/themes/justnews/themer/assets/images/lazy.png)
#define LINQ_H
include
include
include
include
include
include
<set>
include
include
(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
#include <string>
#include
template
void printC(const T& v)
{
for (auto i : v) cout << i << ',';
cout << endl;
}
template
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<:>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<:>string>{"_a", "b"})
.any([](const std::string& s){ return startsWith(s, "_"); }));
assert(!from(std::vector<:>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：）
Original: https://www.cnblogs.com/cbscan/archive/2012/10/20/2732773.html
Author: Scan.
Title: [C++]一份Linq to object的C++实现
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