77 lines
1.6 KiB
C++
77 lines
1.6 KiB
C++
#include <fmt/format.h>
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#include <functional>
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#include <string>
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template <typename T>
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struct Item {
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using value_type = T;
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using const_reference = const T&;
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T value;
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Item<T>* next = nullptr;
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Item<T>* emplace(const_reference value) {
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auto item = new Item<T>{value, next};
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next = item;
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return item;
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}
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void visit(std::function<void(const_reference)> visitor) const {
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visitor(value);
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if (next != nullptr) {
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next->visit(visitor);
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}
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}
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Item<T>* tail() {
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for (auto at = this; at != nullptr; at = at->next) {
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if (at->next == nullptr) {
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return at;
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}
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}
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return nullptr;
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}
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};
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using IntItem = Item<int>;
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template <typename T>
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void dump(const Item<T>* head) {
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head->visit([](const T& value) { fmt::print(" {}", value); });
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fmt::print("\n");
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}
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template <typename T>
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std::string to_string(const Item<T>* head) {
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std::stringstream w;
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head->visit([&w](const T& value) { w << " " << value; });
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return w.str();
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}
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template <typename T>
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Item<T>* make_list(std::initializer_list<T> items) {
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// TODO(michaelh): change to take an initialiser list.
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auto first = new Item<T>{1};
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auto at = first;
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for (const auto& i : items) {
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at = at->emplace(i);
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}
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return first;
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}
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template <typename T>
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Item<T>* filter(Item<T>* head, std::function<bool(int)> predicate) {
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// TODO(michaelh): std::function<bool(T)> doesn't match.
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// TODO(michaelh): how can you mark the return as not-null?
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auto at = &head;
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for (auto at = &head; *at != nullptr;) {
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if (predicate((*at)->value)) {
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*at = (*at)->next;
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} else {
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at = &(*at)->next;
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}
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}
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fmt::print("\n");
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return head;
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}
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