为什么C++常量模板化向量在使用之前没有初始化？

更新：问题是为什么下面的代码(MWE(按原样工作，而不是像我期望的那样工作。

为了个人方便，我创建了以下模板化向量：

// shorthand for loops, etc.
template <size_t N>
const vector<size_t> range = []() {
vector<size_t> res(N);
for (size_t i = 0; i < N; i++) res[i] = i;
cout << "Created range<" << N << ">: [";
for (auto x: res) cout << x << ' ';
cout << ']' << endl;
return res;
}();

因此，我可以进一步编写更多简洁的循环，如下所示：

for (auto i : range<42>) do_something(i);

但是，我意识到(经过一些调试(似乎不能保证在使用前初始化所有必需的range<N>实例！这是相当违反直觉的，所以我认为如果我做错了什么。

更准确地说，我有以下MWE：

#include <bits/stdc++.h>
using namespace std;
template <size_t N>
const vector<size_t> range = []() {
cout << "Initialising range<" << N << ">" << endl;
vector<size_t> result(N);
for (size_t i = 0; i < N; i++) result[i] = i;
return result;
}();
template <size_t K>
class Data {
private:
size_t m_code;
public:
size_t get_code() const { return m_code; }
constexpr static size_t cardinality = K + 1;
explicit Data(size_t code);
const static vector<Data> elems;
};
template <size_t K>
const vector<Data<K>> Data<K>::elems = []() {
cout << "Creating Data elements for K=" << K << endl;
vector<Data<K>> xs;
for (size_t i : range<Data<K>::cardinality>) xs.push_back(Data<K>(i));
return xs;
}();
template <size_t K>
Data<K>::Data(size_t code) {
m_code = code;
cout << "At the moment, range<" << K << "> is [";
for (auto k : range<K>)
cout << k << ' ';  // <<< Shouldn't range<K> be already initialised here?..
cout << "] (len=" << range<K>.size() << ")" << endl;
}
int main() {
cout << ">>> Inside main()" << endl;
constexpr size_t K = 2;
cout << "Data elements:" << endl;
for (const auto &X : Data<K>::elems) {
cout << "Element Data(" << X.get_code() << ")" << endl;
}
cout << "Now, range<" << K << "> is [";
for (auto k : range<K>) cout << k << ' ';
cout << "] (len=" << range<K>.size() << ")" << endl;
}

这将生成以下输出：

Initialising range<3>
Creating Data elements for K=2
At the moment, range<2> is [] (len=0)
At the moment, range<2> is [] (len=0)
At the moment, range<2> is [] (len=0)
Initialising range<2>
>>> Inside main()
Data elements:
Element Data(0)
Element Data(1)
Element Data(2)
Now, range<2> is [0 1 ] (len=2)

我真的不明白为什么它会按原样工作。我的意思是，我希望在使用之前初始化一个const向量(或任何向量！(，因此每当我在代码中使用它时range<2>长度为二。