tensor.hpp

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// Copyright 2025 Eric Hermosis
//
// This file is part of the Tannic Tensor Library.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//  
 
#ifndef TENSOR_HPP
#define TENSOR_HPP 
 
#include <iostream>  
#include <memory>
#include <cassert> 
#include <utility> 
#include <initializer_list> 
 
#include "types.hpp"
#include "shape.hpp" 
#include "strides.hpp" 
#include "buffer.hpp"
#include "slices.hpp" 
#include "views.hpp"
#include "operations.hpp" 
#include "complex.hpp"
#include "graph.hpp"
 
namespace tannic {  
 
class Tensor {
public: 
    using rank_type = uint8_t;      
    using size_type = std::size_t;  
 
    Tensor(type dtype, Shape shape)
    :   dtype_(dtype)
    ,   shape_(shape) 
    ,   strides_(shape_) 
    ,   offset_(0)  {
        nelements_ = std::accumulate(shape_.begin(), shape_.end(), 1ULL, std::multiplies<>{}); 
    }
 
    Tensor(type dtype, Shape shape, Strides strides, std::ptrdiff_t offset = 0)
    :   dtype_(dtype)
    ,   shape_(shape) 
    ,   strides_(strides) 
    ,   offset_(offset)  
    {    
        std::size_t expected = 1;
        for (std::size_t dimension = 0; dimension < rank(); ++dimension) { 
            std::size_t index = rank() - 1 - dimension;   
            if (strides_[index] != expected) {
                is_contiguous_ = false;
            }
            nelements_ *= shape_[index];
            expected *= shape_[index];
        }   
    }
 
 
    template <Expression Expression>
    Tensor(const Expression& expression) {
        *this = expression.forward(); 
    } 
 
    template <Expression Expression>
    Tensor& operator=(const Expression& expression) {
        *this = expression.forward(); 
        return *this;
    }  
 
public:  
 
    type dtype() const { 
        return dtype_; 
    } 
 
    rank_type rank() const { 
        return shape_.rank(); 
    }          
 
    Shape const& shape() const {  
        return shape_; 
    }
 
    Shape::size_type size(int dimension) const {
        return shape_[dimension];
    }
 
    Strides const& strides() const { 
        return strides_; 
    } 
 
    std::ptrdiff_t offset() const {
        return offset_;
    } 
    
    std::size_t nelements() const {  
        return nelements_;
    } 
 
    std::size_t nbytes() const {  
        return nbytesof(dtype_, nelements_);
    } 
 
    bool is_contiguous() const {
        return is_contiguous_;
    }
 
    bool is_singleton() const {
        return (nelements_ == 1);
    }
      
    Tensor& forward() { 
        if (!is_initialized())
            initialize(); 
        return *this;
    } 
 
    Tensor const& forward() const {
        if (!is_initialized())
            initialize(); 
        return *this;
    } 
 
 
public:   
 
    void initialize(Environment environment = Host{}) const;
   
    std::byte* bytes() const {
        return static_cast<std::byte*>(buffer_->address()) + offset_;
    }  
 
    bool is_initialized() const {
        return buffer_ ? true : false;
    } 
 
    Environment const& environment() const {
        if (!is_initialized())
            throw Exception("Cannot get resource of an initializer tensor."); 
        return buffer_->environment();
    }   
 
public: 
    template<typename T>
    Tensor(std::initializer_list<T> const& values)
    :   dtype_(dtypeof<T>())
    ,   shape_({values.size()})
    ,   strides_(shape_)
    ,   offset_(0)
    ,   nelements_(shape_[0]) {
        if (dtype_ == boolean) { 
            initialize();
            std::ptrdiff_t index = 0; 
            for (auto const& value : values) {
                assign((bool const*)(&value), index);
                ++index;
            }
        }
 
        else { 
            initialize();
            size_t index = 0;
            for (auto const& value : values) {
                assign((std::byte const*)(&value), index * dsizeof(dtype_));
                ++index;
            }
        } 
    }
 
    template<typename T>
    Tensor(std::initializer_list<std::initializer_list<T>> const& values)
    :   dtype_(dtypeof<T>())
    ,   shape_({values.size(), values.begin()->size()})
    ,   strides_(shape_)
    ,   offset_(0) 
    ,   nelements_(shape_[0] * shape_[1])
    {
 
        if (dtype_ == boolean) { 
            initialize();
            std::ptrdiff_t index = 0;   
            for (auto const& row : values) {
                if (row.size() != shape_[1])
                    throw Exception("All rows must have the same number of columns");
                for (auto const& value : row) {
                    assign((bool const*)(&value), index);
                    ++index;
                }
            }
        } 
 
        else { 
            initialize(); 
            size_t index = 0;   
            for (auto row : values) {
                if (row.size() != shape_[1])
                    throw Exception("All rows must have the same number of columns");
                for (auto const& value : row) {
                    assign((std::byte const*)(&value), index * dsizeof(dtype_));
                    ++index;
                }
            }
        } 
    }
 
    template<typename T>
    Tensor(std::initializer_list<std::initializer_list<std::initializer_list<T>>> const& values)
    :   dtype_(dtypeof<T>())
    ,   shape_({values.size(), values.begin()->size(), values.begin()->begin()->size()})
    ,   strides_(shape_)
    ,   offset_(0)
    ,   nelements_(shape_[0] * shape_[1] * shape_[2])
        
    {
        if (dtype_ == boolean) { 
            initialize();
            std::ptrdiff_t index = 0;   
            for (auto const& matrix : values) {
                if (matrix.size() != shape_[1])
                    throw Exception("All matrices must have the same number of rows");
                for (auto const& row : matrix) {
                    if (row.size() != shape_[2])
                        throw Exception("All rows must have the same number of columns");
                    for (auto const& value : row) {
                        assign((bool const*)(&value), index);
                        ++index;
                    }
                }
            }
        }
 
        else { 
            initialize(); 
            size_t index = 0;   
            for (auto const& matrix : values) {
                if (matrix.size() != shape_[1])
                    throw Exception("All matrices must have the same number of rows");
                for (auto const& row : matrix) {
                    if (row.size() != shape_[2])
                        throw Exception("All rows must have the same number of columns");
                    for (auto const& value : row) {
                        assign((std::byte const*)(&value), index * dsizeof(dtype_));
                        ++index;
                    }
                }
            }
        } 
    }   
 
 
    template<typename T>
    Tensor(std::initializer_list<std::initializer_list<std::initializer_list<std::initializer_list<T>>>> const& values)
    :    dtype_(dtypeof<T>())
    ,    shape_({
            values.size(),
            values.begin()->size(),
            values.begin()->begin()->size(),
            values.begin()->begin()->begin()->size()
        })
    ,   strides_(shape_)
    ,   offset_(0)
    ,   nelements_(shape_[0] * shape_[1] * shape_[2] * shape_[3])
    {
        
        if (dtype_ == boolean) { 
            initialize();
            std::ptrdiff_t index = 0;
            for (auto const& tensor3D : values) {
                if (tensor3D.size() != shape_[1])
                    throw Exception("All 3D tensors must have the same number of matrices");
                for (auto const& matrix : tensor3D) {
                    if (matrix.size() != shape_[2])
                        throw Exception("All matrices must have the same number of rows");
                    for (auto const& row : matrix) {
                        if (row.size() != shape_[3])
                            throw Exception("All rows must have the same number of columns");
                        for (auto const& value : row) {
                            assign((bool const*)(&value), index);
                            ++index;
                        }
                    }
                }
            }
        }
 
        else {  
            initialize();
 
            size_t index = 0;
            for (auto const& tensor3D : values) {
                if (tensor3D.size() != shape_[1])
                    throw Exception("All 3D tensors must have the same number of matrices");
                for (auto const& matrix : tensor3D) {
                    if (matrix.size() != shape_[2])
                        throw Exception("All matrices must have the same number of rows");
                    for (auto const& row : matrix) {
                        if (row.size() != shape_[3])
                            throw Exception("All rows must have the same number of columns");
                        for (auto const& value : row) {
                            assign((std::byte const*)(&value), index * dsizeof(dtype_));
                            ++index;
                        }
                    }
                }
            } 
        } 
    }
 
 
public: 
    template<typename T>
    void initialize(std::initializer_list<T> values, Environment environment = Host{}) {
        if (!is_contiguous())
            throw Exception("Assign to initializer list supported only for contiguous tensors");
      
        if (rank() != 1 || shape_[0] != values.size())
            throw Exception("Shape mismatch in assignment from initializer_list");
 
        if (!is_initialized()) 
            initialize(environment);
 
        if (dtype_ == boolean) {
            std::ptrdiff_t index = 0;
            for (auto const& value : values) {
                assign((bool const*)(&value), index);
                ++index;
            }
        } 
        
        else { 
            auto fill = [this, &values](auto cast) { 
                using Cast = decltype(cast);
                size_t index = 0;
                for (auto value : values) {
                    if constexpr (std::is_same_v<Cast, float16_t>) { 
                        float as_float = value;
                        float16_t casted = float32_to_float16(as_float);
                        assign(expression::tobytes(casted), index * dsizeof(dtype_));
                    } else { 
                        Cast casted = value;
                        assign(expression::tobytes(casted), index * dsizeof(dtype_));
                    }
                    ++index;
                }
            }; 
 
            switch (dtype_) {
                case int8:    fill(int8_t{});    break;
                case int16:   fill(int16_t{});   break;
                case int32:   fill(int32_t{});   break;
                case int64:   fill(int64_t{});   break;
                case float16: fill(float16_t{}); break;   
                case float32: fill(float{});     break;
                case float64: fill(double{});    break;
                default: throw Exception("Unsupported dtype in assignment");
            } 
        } 
    }
 
    template<typename T>
    void initialize(std::initializer_list<std::initializer_list<T>> const & values, Environment environment = Host{}) {
        if (!is_contiguous())
            throw Exception("Assign to initializer list supported only for contiguous tensors"); 
 
        if (rank() != 2 || shape_[0] != values.size() || shape_[1] != values.begin()->size())
            throw Exception("Shape mismatch in assignment from nested initializer_list"); 
 
        if (!is_initialized()) 
            initialize(environment);
 
        if (dtype_ == boolean) {
            std::ptrdiff_t index = 0;
            for (auto const& row : values) {
                if (row.size() != shape_[1])
                    throw Exception("Row length mismatch in assignment from initializer_list");
                for (auto const& value : row) {
                    assign((bool const*)(&value), index);
                    ++index;
                }
            } 
        }
 
        else { 
            auto fill = [this, &values](auto cast) { 
                using Cast = decltype(cast);
                size_t index = 0;
                for (auto const& row : values) {
                    if (row.size() != shape_[1])
                        throw Exception("Row length mismatch in assignment from initializer_list");
 
                    for (auto value : row) {
                        if constexpr (std::is_same_v<Cast, float16_t>) {
                            float as_float = value;
                            float16_t casted = float32_to_float16(as_float);
                            assign(expression::tobytes(casted), index * dsizeof(dtype_));
                        } else {
                            Cast casted = value;
                            assign(expression::tobytes(casted), index * dsizeof(dtype_));
                        }
                        ++index;
                    }
                }
            };
 
            switch (dtype_) {
                case int8:    fill(int8_t{});    break;
                case int16:   fill(int16_t{});   break;
                case int32:   fill(int32_t{});   break;
                case int64:   fill(int64_t{});   break;
                case float16: fill(float16_t{}); break;   
                case float32: fill(float{});     break;
                case float64: fill(double{});    break;
                default: throw Exception("Unsupported dtype in assignment");
            } 
        }  
    }
 
 
 
 
    template<typename T>
    void initialize(std::initializer_list<std::initializer_list<std::initializer_list<T>>> const& values, Environment environment = Host{}) {
        if (!is_contiguous())
            throw Exception("Assign to initializer list supported only for contiguous tensors");
 
        if (rank() != 3 
            || shape_[0] != values.size() 
            || shape_[1] != values.begin()->size() 
            || shape_[2] != values.begin()->begin()->size())
            throw Exception("Shape mismatch in assignment from triple-nested initializer_list");
 
        if (!is_initialized()) 
            initialize(environment);
 
        if (dtype_ == boolean) {
            std::ptrdiff_t index = 0;
            for (auto const& matrix : values) {
                if (matrix.size() != shape_[1])
                    throw Exception("Matrix row count mismatch");
                for (auto const& row : matrix) {
                    if (row.size() != shape_[2])
                        throw Exception("Row length mismatch");
                    for (auto const& value : row) {
                        assign((bool const*)(&value), index);
                        ++index;
                    }
                }
            }
        }
 
        else { 
            auto fill = [this, &values](auto cast) { 
                using Cast = decltype(cast);
                size_t index = 0;
                for (auto const& matrix : values) {
                    if (matrix.size() != shape_[1])
                        throw Exception("Matrix row count mismatch");
                    for (auto const& row : matrix) {
                        if (row.size() != shape_[2])
                            throw Exception("Row length mismatch");
                        for (auto value : row) {
                            if constexpr (std::is_same_v<Cast, float16_t>) {
                                float as_float = value;
                                float16_t casted = float32_to_float16(as_float);
                                assign(expression::tobytes(casted), index * dsizeof(dtype_));
                            } else {
                                Cast casted = value;
                                assign(expression::tobytes(casted), index * dsizeof(dtype_));
                            }
                            ++index;
                        }
                    }
                }
            };
 
            switch (dtype_) {
                case int8:    fill(int8_t{});    break;
                case int16:   fill(int16_t{});   break;
                case int32:   fill(int32_t{});   break;
                case int64:   fill(int64_t{});   break;
                case float16: fill(float16_t{}); break;   
                case float32: fill(float{});     break;
                case float64: fill(double{});    break;
                default: throw Exception("Unsupported dtype in assignment");
            } 
        } 
} 
 
    template<typename T>
    void initialize(std::initializer_list<std::initializer_list<std::initializer_list<std::initializer_list<T>>>> values, Environment environment = Host{}) {
        if (!is_contiguous())
            throw Exception("Assign to initializer list supported only for contiguous tensors");
 
        if (rank() != 4 
            || shape_[0] != values.size() 
            || shape_[1] != values.begin()->size() 
            || shape_[2] != values.begin()->begin()->size() 
            || shape_[3] != values.begin()->begin()->begin()->size())
            throw Exception("Shape mismatch in assignment from quadruple-nested initializer_list");
 
        if (!is_initialized()) 
            initialize(environment);
 
        if (dtype_ == boolean) {
            std::ptrdiff_t index = 0;
            for (auto const& tensor3D : values) {
                if (tensor3D.size() != shape_[1])
                    throw Exception("3D tensor count mismatch");
 
                for (auto const& matrix : tensor3D) {
                    if (matrix.size() != shape_[2])
                        throw Exception("Matrix row count mismatch");
 
                    for (auto const& row : matrix) {
                        if (row.size() != shape_[3])
                            throw Exception("Row length mismatch");
 
                        for (auto const& value : row) {
                            assign((bool const*)(&value), index);
                            ++index;
                        }
                    }
                }
            } 
        }  
        
        else { 
            auto fill = [this, &values](auto cast) { 
                using Cast = decltype(cast);
                size_t index = 0;
                for (auto const& tensor3D : values) {
                    if (tensor3D.size() != shape_[1])
                        throw Exception("3D tensor count mismatch");
 
                    for (auto const& matrix : tensor3D) {
                        if (matrix.size() != shape_[2])
                            throw Exception("Matrix row count mismatch");
 
                        for (auto const& row : matrix) {
                            if (row.size() != shape_[3])
                                throw Exception("Row length mismatch");
 
                            for (auto value : row) {
                                if constexpr (std::is_same_v<Cast, float16_t>) {
                                    float as_float = value;
                                    float16_t casted = float32_to_float16(as_float);
                                    assign(expression::tobytes(casted), index * dsizeof(dtype_));
                                } else {
                                    Cast casted = value;
                                    assign(expression::tobytes(casted), index * dsizeof(dtype_));
                                }
                                ++index;
                            }
                        }
                    }
                }
            };
 
            switch (dtype_) {
                case int8:    fill(int8_t{});    break;
                case int16:   fill(int16_t{});   break;
                case int32:   fill(int32_t{});   break;
                case int64:   fill(int64_t{});   break;
                case float16: fill(float16_t{}); break;  
                case float32: fill(float{});     break;
                case float64: fill(double{});    break;
                default: throw Exception("Unsupported dtype in assignment");
            } 
        }  
    } 
    
public: 
 
    template<Integral Index>
    auto operator[](Index index) const {   
        if (!is_initialized())
            initialize(); 
        return expression::Slice<Tensor, Index>(*this, std::make_tuple(index));
    }
 
    auto operator[](indexing::Range range) const { 
        if (!is_initialized())
            initialize(); 
        return expression::Slice<Tensor, indexing::Range>(*this, std::make_tuple(range));
    } 
 
    template<class ... Indexes>
    auto operator[](Indexes... indexes) const {
        if (!is_initialized())
            initialize(); 
        return expression::Slice<Tensor, Indexes...>(*this, std::make_tuple(indexes...));
    } 
 
 
    auto transpose(int first = -1, int second = -2) const {
        if (!is_initialized())
            initialize(); 
        return expression::Transpose<Tensor>(*this, std::make_pair<int, int>(std::move(first), std::move(second)));
    }  
 
    template<Integral ... Indexes>
    auto permute(Indexes... indexes) const {
        if (!is_initialized())
            initialize(); 
        return expression::Permutation<Tensor, Indexes...>(*this, std::make_tuple(indexes...));
    } 
 
    template<Integral ... Sizes>
    auto view(Sizes... sizes) const {
        if (!is_initialized())
            initialize(); 
        return expression::View<Tensor>(*this, sizes...);
    } 
 
    auto squeeze() const {
        if (!is_initialized())
            initialize();
        return expression::Squeeze<Tensor>(*this);
    }
 
 
    template<Integral... Axes>
    auto unsqueeze(Axes... axes) {
        return expression::Unsqueeze<Tensor>(*this, axes...);
    }
 
public:
 
    Tensor(type dtype, Shape shape, std::ptrdiff_t offset, std::shared_ptr<Buffer> storage)
    :   dtype_(dtype)
    ,   shape_(shape) 
    ,   strides_(shape)
    ,   offset_(offset)   
    ,   buffer_(std::move(storage)) 
    {
        nelements_ = std::accumulate(shape_.begin(), shape_.end(), 1ULL, std::multiplies<>{}); 
        node_ = std::make_shared<Node>(*this);
    }
 
    Tensor(type dtype, Shape shape, Strides strides, std::ptrdiff_t offset, std::shared_ptr<Buffer> storage)
    :   dtype_(dtype)
    ,   shape_(shape) 
    ,   strides_(strides)
    ,   offset_(offset)   
    ,   buffer_(std::move(storage)) 
    {  
        std::size_t expected = 1;
        for (std::size_t dimension = 0; dimension < rank(); ++dimension) { 
            std::size_t index = rank() - 1 - dimension;   // walk backward logically
            if (strides_[index] != expected) {
                is_contiguous_ = false;
            }
            nelements_ *= shape_[index];
            expected *= shape_[index];
        }   
        node_ = std::make_shared<Node>(*this);
    }
 
protected:    
    template <Expression Source, class... Indexes> 
    friend class expression::Slice;
 
    template <Expression Source> 
    friend class expression::Transpose;
 
    template <Expression Source>
    friend class expression::View; 
 
    template <Expression Source>
    friend class expression::Squeeze; 
 
    template <Expression Source>
    friend class expression::Unsqueeze;
 
    template <Expression Source, Integral... Indexes> 
    friend class expression::Permutation; 
 
    template <Expression Source>
    friend class expression::Expansion;
 
    template <Expression Source>
    friend class expression::Flatten;
 
    template <class Coordinates, Expression... Sources>
    friend class expression::Complexification;
 
    template <Expression Source>
    friend class expression::Realification;
 
    void assign(std::byte const*, std::ptrdiff_t); 
    void assign(bool const*, std::ptrdiff_t); 
 
    bool compare(std::byte const*, std::ptrdiff_t) const; 
     
 
public:
    Node* node() const { 
        return node_.get();
    } 
 
private:
    // Note: I didn't decide yet if put all this inside Node.
    // That will speed tensor copies but disallow make the tensors
    // only runtime since shared ptrs don't support constexpr.
    // For now kernel optimization is more important. 
    type dtype_;
    Shape shape_; 
    Strides strides_; 
    std::size_t nelements_ = 1;
    std::ptrdiff_t offset_ = 0;    
    mutable std::shared_ptr<Buffer> buffer_ = nullptr;
    mutable std::shared_ptr<Node> node_ = nullptr;
    bool is_contiguous_ = true;
};    
 
std::ostream& operator<<(std::ostream& ostream, Tensor const& tensor);  
 
template<Expression Source> 
inline std::ostream& operator<<(std::ostream& ostream, Source source) {
    Tensor tensor = source.forward();  
    ostream << tensor;
    return ostream;
} 
 
template<class Operation, Expression Operand>
Tensor operation::Unary<Operation, Operand>::forward() const { 
    Tensor result(dtype(), shape(), strides(), offset());  
    operation.forward(operand, result);
    return result;
}
 
template<Operator Operation, Expression Operand, Expression Cooperand>
Tensor operation::Binary<Operation, Operand, Cooperand>::forward() const {
    Tensor result(dtype(), shape(), strides());
    operation.forward(operand, cooperand, result);
    return result;
}  
 
template<Expression Source>
Tensor expression::View<Source>::forward() const { 
    Tensor source = source_.forward();
    return Tensor(dtype(), shape(), strides(), offset(), source.buffer_);
}
 
template<Expression Source>
Tensor expression::Squeeze<Source>::forward() const { 
    Tensor source = source_.forward();
    return Tensor(dtype(), shape(), strides(), offset(), source.buffer_);
}
 
template<Expression Source>
Tensor expression::Unsqueeze<Source>::forward() const { 
    Tensor source = source_.forward();
    return Tensor(dtype(), shape(), strides(), offset(), source.buffer_);
}
 
template<Expression Source>
Tensor expression::Flatten<Source>::forward() const { 
    Tensor source = source_.forward();
    return Tensor(dtype(), shape(), strides(), offset(), source.buffer_);
} 
 
template<Expression Source, Integral... Indexes>
Tensor expression::Permutation<Source, Indexes...>::forward() const {   
    Tensor source = source_.forward();
    return Tensor(dtype(), shape(), strides(), offset(), source.buffer_);
}         
 
template<Expression Source>
Tensor expression::Transpose<Source>::forward() const { 
    Tensor source = source_.forward(); 
    return Tensor(dtype(), shape(), strides(), offset(), source.buffer_);
}   
 
template<Expression Source>
Tensor expression::Expansion<Source>::forward() const { 
    Tensor source = source_.forward();
    return Tensor(dtype(), shape(), strides(), offset(), source.buffer_);
}
 
template<Expression Source, class... Indexes>
Tensor expression::Slice<Source, Indexes...>::forward() const {   
    Tensor source = source_.forward();
    return Tensor(dtype(), shape(), strides(), offset(), source.buffer_);
}         
 
template<Expression Source, class... Indexes>
void expression::Slice<Source, Indexes...>::assign(std::byte const* value, std::ptrdiff_t offset) { 
    if constexpr (Trait<Source>::is_assignable) {
        source_.assign(value, offset); 
    } 
 
    else {
        Tensor tensor = forward();
        tensor.assign(value, offset);
    }
}  
 
template<Expression Source, class... Indexes>
void expression::Slice<Source, Indexes...>::assign(bool const* value, std::ptrdiff_t offset) { 
    if constexpr (Trait<Source>::is_assignable) {
        source_.assign(value, offset); 
    } 
 
    else {
        Tensor tensor = forward();
        tensor.assign(value, offset);
    }
}  
 
 
template<Expression Source, class... Indexes>
bool expression::Slice<Source, Indexes...>::compare(std::byte const* value, std::ptrdiff_t offset) const { 
    if constexpr (Trait<Source>::is_comparable) {
        return source_.compare(value, offset); 
    } 
 
    else {
        Tensor tensor = forward();
        return tensor.compare(value, offset);
    }
}  
 
template<class Coordinates, Expression Source>
Tensor expression::Complexification<Coordinates, Source>::forward() const {
    Tensor real = source.forward();
    Tensor complex(dtype(), shape(), strides(), offset(), real.buffer_); 
    return complex; 
} 
 
template<class Coordinates, Expression Real, Expression Imaginary>
Tensor expression::Complexification<Coordinates, Real, Imaginary>::forward() const {  
    Tensor result(dtype(), shape(), strides(), offset());
    Coordinates::forward(real.forward(), imaginary.forward(), result);
    return result;
} 
 
template<Expression Source>
Tensor expression::Realification<Source>::forward() const {
    Tensor complex = source.forward();
    Tensor real(dtype(), shape(), strides(), offset(), complex.buffer_); 
    return real; 
}
 
} // namespace tannic
 
#endif // TENSOR_HPP