116 lines
5.0 KiB
Markdown
116 lines
5.0 KiB
Markdown
[template.indirect.array]
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# 29 Numerics library [[numerics]](./#numerics)
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## 29.6 Numeric arrays [[numarray]](numarray#template.indirect.array)
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### 29.6.9 Class template indirect_array [template.indirect.array]
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#### [29.6.9.1](#overview) Overview [[template.indirect.array.overview]](template.indirect.array.overview)
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[ð](#lib:indirect_array)
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namespace std {template<class T> class indirect_array {public:using value_type = T; void operator= (const valarray<T>&) const; void operator*= (const valarray<T>&) const; void operator/= (const valarray<T>&) const; void operator%= (const valarray<T>&) const; void operator+= (const valarray<T>&) const; void operator-= (const valarray<T>&) const; void operator^= (const valarray<T>&) const; void operator&= (const valarray<T>&) const; void operator|= (const valarray<T>&) const; void operator<<=(const valarray<T>&) const; void operator>>=(const valarray<T>&) const;
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indirect_array(const indirect_array&); ~indirect_array(); const indirect_array& operator=(const indirect_array&) const; void operator=(const T&) const;
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indirect_array() = delete; // as implied by declaring copy constructor above};}
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[1](#overview-1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L9029)
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This template is a helper template used by the indirect subscript operator
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[ð](#lib:operator%5b%5d,indirect_array)
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`indirect_array<T> valarray<T>::operator[](const valarray<size_t>&);
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`
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[2](#overview-2)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L9036)
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It has reference semantics to a subset of an array specified by anindirect_array[.](#overview-2.sentence-1)
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Thus, the expressiona[indirect] = b; has the effect of assigning the elements ofb to the elements ina whose indices appear inindirect[.](#overview-2.sentence-2)
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#### [29.6.9.2](#indirect.array.assign) Assignment [[indirect.array.assign]](indirect.array.assign)
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[ð](#lib:operator=,indirect_array)
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`void operator=(const valarray<T>&) const;
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const indirect_array& operator=(const indirect_array&) const;
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`
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[1](#indirect.array.assign-1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L9057)
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These assignment operators have reference semantics, assigning the values
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of the argument array elements to selected elements of thevalarray<T> object to which it refers[.](#indirect.array.assign-1.sentence-1)
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[2](#indirect.array.assign-2)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L9063)
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If theindirect_array specifies an element in thevalarray<T> object to which it refers more than once, the behavior is undefined[.](#indirect.array.assign-2.sentence-1)
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[3](#indirect.array.assign-3)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L9071)
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[*Example [1](#indirect.array.assign-example-1)*:
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int addr[] = {2, 3, 1, 4, 4};
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valarray<size_t> indirect(addr, 5);
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valarray<double> a(0., 10), b(1., 5);
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a[indirect] = b; results in undefined behavior since element 4 is specified twice in the
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indirection[.](#indirect.array.assign-3.sentence-1)
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â *end example*]
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#### [29.6.9.3](#indirect.array.comp.assign) Compound assignment [[indirect.array.comp.assign]](indirect.array.comp.assign)
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[ð](#lib:operator*=,indirect_array)
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`void operator*= (const valarray<T>&) const;
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void operator/= (const valarray<T>&) const;
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void operator%= (const valarray<T>&) const;
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void operator+= (const valarray<T>&) const;
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void operator-= (const valarray<T>&) const;
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void operator^= (const valarray<T>&) const;
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void operator&= (const valarray<T>&) const;
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void operator|= (const valarray<T>&) const;
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void operator<<=(const valarray<T>&) const;
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void operator>>=(const valarray<T>&) const;
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`
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[1](#indirect.array.comp.assign-1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L9110)
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These compound assignments have reference semantics, applying the indicated
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operation to the elements of the argument array and selected elements of thevalarray<T> object to which theindirect_array object refers[.](#indirect.array.comp.assign-1.sentence-1)
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[2](#indirect.array.comp.assign-2)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L9118)
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If theindirect_array specifies an element in thevalarray<T> object to which it refers more than once,
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the behavior is undefined[.](#indirect.array.comp.assign-2.sentence-1)
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#### [29.6.9.4](#indirect.array.fill) Fill function [[indirect.array.fill]](indirect.array.fill)
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[ð](#lib:operator=,indirect_array_)
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`void operator=(const T&) const;
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`
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[1](#indirect.array.fill-1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L9136)
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This function has reference semantics, assigning the value of its argument
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to the elements of thevalarray<T> object to which theindirect_array object refers[.](#indirect.array.fill-1.sentence-1)
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