SkAdvancedTypefaceMetrics: abstract out linked list

src/pdf/SkSinglyLinkedList.h

-/*
- * Copyright 2016 Google Inc.
- *
- * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file.
- */
-#ifndef SkSinglyLinkedList_DEFINED
-#define SkSinglyLinkedList_DEFINED
-
-#include <utility>
-
-#include "SkTypes.h"
-
-template <typename T> class SkSinglyLinkedList {
-    struct Node;
-public:
-    SkSinglyLinkedList() : fHead(nullptr), fTail(nullptr) {}
-    ~SkSinglyLinkedList() { this->reset(); }
-    void reset() {
-        SkASSERT(fHead != nullptr || nullptr == fTail);
-        // Use a while loop rather than recursion to avoid stack overflow.
-        Node* node = fHead;
-        while (node) {
-            Node* next = node->fNext;
-            SkASSERT(next != nullptr || node == fTail);
-            delete node;
-            node = next;
-        }
-        fHead = nullptr;
-        fTail = nullptr;
-    }
-    T* back() { return fTail ? &fTail->fData : nullptr; }
-    T* front() { return fHead ? &fHead->fData : nullptr; }
-    #ifdef SK_DEBUG
-    int count() {  // O(n), debug only.
-        int count = 0;
-        for (Node* node = fHead; node; node = node->fNext) {
-            ++count;
-        }
-        return count;
-    }
-    #endif
-    void pop_front() {
-        if (Node* node = fHead) {
-            fHead = node->fNext;
-            delete node;
-            if (fHead == nullptr) {
-                fTail = nullptr;
-            }
-        }
-    }
-    template <class... Args> T* emplace_front(Args&&... args) {
-        Node* n = new Node(std::forward<Args>(args)...);
-        n->fNext = fHead;
-        if (!fTail) {
-            fTail = n;
-            SkASSERT(!fHead);
-        }
-        fHead = n;
-        return &n->fData;
-    }
-    template <class... Args> T* emplace_back(Args&&... args) {
-        Node* n = new Node(std::forward<Args>(args)...);
-        if (fTail) {
-            fTail->fNext = n;
-        } else {
-            fHead = n;
-        }
-        fTail = n;
-        return &n->fData;
-    }
-    class ConstIter {
-    public:
-        void operator++() { fNode = fNode->fNext; }
-        const T& operator*() const { return fNode->fData; }
-        bool operator!=(const ConstIter& rhs) const { return fNode != rhs.fNode; }
-        ConstIter(const Node* n) : fNode(n) {}
-    private:
-        const Node* fNode;
-    };
-    ConstIter begin() const { return ConstIter(fHead); }
-    ConstIter end() const { return ConstIter(nullptr); }
-
-private:
-    struct Node {
-        T fData;
-        Node* fNext;
-        template <class... Args>
-        Node(Args&&... args) : fData(std::forward<Args>(args)...), fNext(nullptr) {}
-    };
-    Node* fHead;
-    Node* fTail;
-    SkSinglyLinkedList(const SkSinglyLinkedList<T>&) = delete;
-    SkSinglyLinkedList& operator=(const SkSinglyLinkedList<T>&) = delete;
-};
-#endif  // SkSinglyLinkedList_DEFINED