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Merge pull request #104055 from Ivorforce/fixed-vector
Core: Add `FixedVector` template - a collection that can be used completely on the stack.
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‎core/templates/fixed_vector.h‎

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/**************************************************************************/
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/* fixed_vector.h */
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/**************************************************************************/
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/* This file is part of: */
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/* GODOT ENGINE */
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/* https://godotengine.org */
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/**************************************************************************/
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/* Copyright (c) 2014-present Godot Engine contributors (see AUTHORS.md). */
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/* Copyright (c) 2007-2014 Juan Linietsky, Ariel Manzur. */
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/* */
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/* Permission is hereby granted, free of charge, to any person obtaining */
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/* a copy of this software and associated documentation files (the */
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/* "Software"), to deal in the Software without restriction, including */
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/* without limitation the rights to use, copy, modify, merge, publish, */
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/* distribute, sublicense, and/or sell copies of the Software, and to */
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/* permit persons to whom the Software is furnished to do so, subject to */
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/* the following conditions: */
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/* */
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/* The above copyright notice and this permission notice shall be */
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/* included in all copies or substantial portions of the Software. */
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/* */
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/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, */
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/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF */
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/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. */
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/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY */
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/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, */
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/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE */
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/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. */
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/**************************************************************************/
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#pragma once
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/**
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* A high performance Vector of fixed capacity.
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* Especially useful if you need to create an array on the stack, to
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* prevent dynamic allocations (especially in bottleneck code).
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*
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* Choose CAPACITY such that it is enough for all elements that could be added through all branches.
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*
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*/
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template <class T, uint32_t CAPACITY>
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class FixedVector {
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// This declaration allows us to access other FixedVector's private members.
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template <class T_, uint32_t CAPACITY_>
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friend class FixedVector;
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uint32_t _size = 0;
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alignas(T) uint8_t _data[CAPACITY * sizeof(T)];
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constexpr static uint32_t DATA_PADDING = MAX(alignof(T), alignof(uint32_t)) - alignof(uint32_t);
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public:
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_FORCE_INLINE_ constexpr FixedVector() = default;
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constexpr FixedVector(std::initializer_list<T> p_init) {
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ERR_FAIL_COND(p_init.size() > CAPACITY);
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for (const T &element : p_init) {
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memnew_placement(ptr() + _size++, T(element));
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}
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}
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template <uint32_t p_capacity>
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constexpr FixedVector(const FixedVector<T, p_capacity> &p_from) {
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ERR_FAIL_COND(p_from.size() > CAPACITY);
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if constexpr (std::is_trivially_copyable_v<T>) {
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// Copy size and all provided elements at once.
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memcpy((void *)&_size, (void *)&p_from._size, sizeof(_size) + DATA_PADDING + p_from.size() * sizeof(T));
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} else {
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for (const T &element : p_from) {
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memnew_placement(ptr() + _size++, T(element));
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}
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}
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}
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template <uint32_t p_capacity>
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constexpr FixedVector(FixedVector<T, p_capacity> &&p_from) {
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ERR_FAIL_COND(p_from.size() > CAPACITY);
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// Copy size and all provided elements at once.
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// Note: Assumes trivial relocatability.
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memcpy((void *)&_size, (void *)&p_from._size, sizeof(_size) + DATA_PADDING + p_from.size() * sizeof(T));
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p_from._size = 0;
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}
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~FixedVector() {
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if constexpr (!std::is_trivially_destructible_v<T>) {
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for (uint32_t i = 0; i < _size; i++) {
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ptr()[i].~T();
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}
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}
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}
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_FORCE_INLINE_ constexpr T *ptr() { return (T *)(_data); }
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_FORCE_INLINE_ constexpr const T *ptr() const { return (const T *)(_data); }
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_FORCE_INLINE_ constexpr operator Span<T>() const { return Span<T>(ptr(), size()); }
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_FORCE_INLINE_ constexpr Span<T> span() const { return operator Span<T>(); }
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_FORCE_INLINE_ constexpr uint32_t size() const { return _size; }
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_FORCE_INLINE_ constexpr bool is_empty() const { return !_size; }
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_FORCE_INLINE_ constexpr bool is_full() const { return _size == CAPACITY; }
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_FORCE_INLINE_ constexpr uint32_t capacity() const { return CAPACITY; }
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_FORCE_INLINE_ constexpr void clear() { resize_initialized(0); }
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/// Changes the size of the vector.
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/// If p_size > size(), constructs new elements.
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/// If p_size < size(), destructs new elements.
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constexpr Error resize_initialized(uint32_t p_size) {
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if (p_size > _size) {
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ERR_FAIL_COND_V(p_size > CAPACITY, ERR_OUT_OF_MEMORY);
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memnew_arr_placement<true>(ptr() + _size, p_size - _size);
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} else if (p_size < _size) {
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if constexpr (!std::is_trivially_destructible_v<T>) {
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for (uint32_t i = p_size; i < _size; i++) {
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ptr()[i].~T();
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}
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}
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}
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_size = p_size;
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return OK;
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}
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/// Changes the size of the vector.
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/// The initializer of new elements is skipped, making this function faster than resize_initialized.
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/// The caller is required to initialize the new values.
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constexpr Error resize_uninitialized(uint32_t p_size) {
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static_assert(std::is_trivially_destructible_v<T>, "resize_uninitialized is unsafe to call if T is not trivially destructible.");
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ERR_FAIL_COND_V(p_size > CAPACITY, ERR_OUT_OF_MEMORY);
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_size = p_size;
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return OK;
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}
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constexpr void push_back(const T &p_val) {
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ERR_FAIL_COND(_size >= CAPACITY);
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memnew_placement(ptr() + _size, T(p_val));
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_size++;
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}
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constexpr void pop_back() {
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ERR_FAIL_COND(_size == 0);
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_size--;
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ptr()[_size].~T();
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}
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// NOTE: Subscripts sanity check the bounds to avoid undefined behavior.
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// This is slower than direct buffer access and can prevent autovectorization.
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// If the bounds are known, use ptr() subscript instead.
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constexpr const T &operator[](uint32_t p_index) const {
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CRASH_COND(p_index >= _size);
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return ptr()[p_index];
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}
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constexpr T &operator[](uint32_t p_index) {
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CRASH_COND(p_index >= _size);
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return ptr()[p_index];
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}
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_FORCE_INLINE_ constexpr T *begin() { return ptr(); }
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_FORCE_INLINE_ constexpr T *end() { return ptr() + _size; }
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_FORCE_INLINE_ constexpr const T *begin() const { return ptr(); }
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_FORCE_INLINE_ constexpr const T *end() const { return ptr() + _size; }
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};

‎tests/core/templates/test_fixed_vector.h‎

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/**************************************************************************/
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/* test_fixed_vector.h */
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/**************************************************************************/
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/* This file is part of: */
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/* GODOT ENGINE */
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/* https://godotengine.org */
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/**************************************************************************/
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/* Copyright (c) 2014-present Godot Engine contributors (see AUTHORS.md). */
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/* Copyright (c) 2007-2014 Juan Linietsky, Ariel Manzur. */
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/* */
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/* Permission is hereby granted, free of charge, to any person obtaining */
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/* a copy of this software and associated documentation files (the */
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/* "Software"), to deal in the Software without restriction, including */
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/* without limitation the rights to use, copy, modify, merge, publish, */
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/* distribute, sublicense, and/or sell copies of the Software, and to */
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/* permit persons to whom the Software is furnished to do so, subject to */
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/* the following conditions: */
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/* */
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/* The above copyright notice and this permission notice shall be */
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/* included in all copies or substantial portions of the Software. */
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/* */
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/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, */
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/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF */
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/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. */
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/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY */
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/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, */
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/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE */
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/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. */
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/**************************************************************************/
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#pragma once
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#include "core/templates/fixed_vector.h"
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#include "tests/test_macros.h"
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namespace TestFixedVector {
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TEST_CASE("[FixedVector] Basic Checks") {
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FixedVector<uint16_t, 1> vector;
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CHECK_EQ(vector.capacity(), 1);
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CHECK_EQ(vector.size(), 0);
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CHECK(vector.is_empty());
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CHECK(!vector.is_full());
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vector.push_back(5);
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CHECK_EQ(vector.size(), 1);
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CHECK_EQ(vector[0], 5);
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CHECK_EQ(vector.ptr()[0], 5);
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CHECK(!vector.is_empty());
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CHECK(vector.is_full());
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vector.pop_back();
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CHECK_EQ(vector.size(), 0);
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CHECK(vector.is_empty());
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CHECK(!vector.is_full());
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FixedVector<uint16_t, 2> vector1 = { 1, 2 };
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CHECK_EQ(vector1.capacity(), 2);
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CHECK_EQ(vector1.size(), 2);
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CHECK_EQ(vector1[0], 1);
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CHECK_EQ(vector1[1], 2);
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FixedVector<uint16_t, 3> vector2(vector1);
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CHECK_EQ(vector2.capacity(), 3);
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CHECK_EQ(vector2.size(), 2);
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CHECK_EQ(vector2[0], 1);
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CHECK_EQ(vector2[1], 2);
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FixedVector<Variant, 3> vector_variant;
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CHECK_EQ(vector_variant.size(), 0);
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CHECK_EQ(vector_variant.capacity(), 3);
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vector_variant.resize_initialized(3);
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vector_variant[0] = "Test";
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vector_variant[1] = 1;
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CHECK_EQ(vector_variant.capacity(), 3);
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CHECK_EQ(vector_variant.size(), 3);
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CHECK_EQ(vector_variant[0], "Test");
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CHECK_EQ(vector_variant[1], Variant(1));
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CHECK_EQ(vector_variant[2].get_type(), Variant::NIL);
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}
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TEST_CASE("[FixedVector] Alignment Checks") {
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FixedVector<uint16_t, 4> vector_uint16;
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vector_uint16.resize_uninitialized(4);
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CHECK((size_t)&vector_uint16[0] % alignof(uint16_t) == 0);
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CHECK((size_t)&vector_uint16[1] % alignof(uint16_t) == 0);
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CHECK((size_t)&vector_uint16[2] % alignof(uint16_t) == 0);
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CHECK((size_t)&vector_uint16[3] % alignof(uint16_t) == 0);
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FixedVector<uint32_t, 4> vector_uint32;
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vector_uint32.resize_uninitialized(4);
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CHECK((size_t)&vector_uint32[0] % alignof(uint32_t) == 0);
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CHECK((size_t)&vector_uint32[1] % alignof(uint32_t) == 0);
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CHECK((size_t)&vector_uint32[2] % alignof(uint32_t) == 0);
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CHECK((size_t)&vector_uint32[3] % alignof(uint32_t) == 0);
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FixedVector<uint64_t, 4> vector_uint64;
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vector_uint64.resize_uninitialized(4);
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CHECK((size_t)&vector_uint64[0] % alignof(uint64_t) == 0);
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CHECK((size_t)&vector_uint64[1] % alignof(uint64_t) == 0);
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CHECK((size_t)&vector_uint64[2] % alignof(uint64_t) == 0);
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CHECK((size_t)&vector_uint64[3] % alignof(uint64_t) == 0);
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}
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} //namespace TestFixedVector

‎tests/test_main.cpp‎

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#include "tests/core/string/test_translation_server.h"
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#include "tests/core/templates/test_a_hash_map.h"
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#include "tests/core/templates/test_command_queue.h"
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#include "tests/core/templates/test_fixed_vector.h"
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#include "tests/core/templates/test_hash_map.h"
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#include "tests/core/templates/test_hash_set.h"
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#include "tests/core/templates/test_list.h"

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