160 lines
5.0 KiB
Markdown
160 lines
5.0 KiB
Markdown
[valarray.cons]
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# 29 Numerics library [[numerics]](./#numerics)
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## 29.6 Numeric arrays [[numarray]](numarray#valarray.cons)
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### 29.6.2 Class template valarray [[template.valarray]](template.valarray#valarray.cons)
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#### 29.6.2.2 Constructors [valarray.cons]
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[ð](#lib:valarray,constructor)
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`valarray();
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`
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[1](#1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7333)
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*Effects*: Constructs a valarray that has zero length[.](#1.sentence-1)[249](#footnote-249 "This default constructor is essential, since arrays of valarray can be useful. After initialization, the length of an empty array can be increased with the resize member function.")
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[ð](#lib:valarray,constructor_)
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`explicit valarray(size_t n);
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`
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[2](#2)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7354)
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*Effects*: Constructs a valarray that has length n[.](#2.sentence-1)
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Each element of the array is [value-initialized](dcl.init#def:value-initialization "9.5 Initializers [dcl.init]")[.](#2.sentence-2)
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[ð](#lib:valarray,constructor__)
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`valarray(const T& v, size_t n);
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`
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[3](#3)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7366)
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*Effects*: Constructs a valarray that has length n[.](#3.sentence-1)
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Each element of the array is initialized with v[.](#3.sentence-2)
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[ð](#lib:valarray,constructor___)
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`valarray(const T* p, size_t n);
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`
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[4](#4)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7379)
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*Preconditions*: [p, p + n) is a valid range[.](#4.sentence-1)
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[5](#5)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7383)
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*Effects*: Constructs a valarray that has length n[.](#5.sentence-1)
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The values of the elements of the array are initialized with the
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firstn values pointed to by the first argument[.](#5.sentence-2)[250](#footnote-250 "This constructor is the preferred method for converting a C array to a valarray object.")
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[ð](#lib:valarray,constructor____)
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`valarray(const valarray& v);
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`
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[6](#6)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7404)
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*Effects*: Constructs a valarray that has the same length as v[.](#6.sentence-1)
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The elements are initialized with the values of the corresponding
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elements of v[.](#6.sentence-2)[251](#footnote-251 "This copy constructor creates a distinct array rather than an alias. Implementations in which arrays share storage are permitted, but they would need to implement a copy-on-reference mechanism to ensure that arrays are conceptually distinct.")
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[ð](#lib:valarray,constructor_____)
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`valarray(valarray&& v) noexcept;
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`
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[7](#7)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7424)
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*Effects*: Constructs a valarray that has the same length as v[.](#7.sentence-1)
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The elements are initialized with the values of the corresponding
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elements of v[.](#7.sentence-2)
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[8](#8)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7430)
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*Complexity*: Constant[.](#8.sentence-1)
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[ð](#lib:valarray,constructor______)
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`valarray(initializer_list<T> il);
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`
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[9](#9)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7441)
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*Effects*: Equivalent to valarray(il.begin(), il.size())[.](#9.sentence-1)
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[ð](#lib:valarray,constructor_______)
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`valarray(const slice_array<T>&);
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valarray(const gslice_array<T>&);
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valarray(const mask_array<T>&);
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valarray(const indirect_array<T>&);
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`
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[10](#10)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7455)
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These conversion constructors convert one of the four reference templates
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to avalarray[.](#10.sentence-1)
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[ð](#lib:valarray,destructor)
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`~valarray();
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`
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[11](#11)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L7467)
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*Effects*: The destructor is applied to every element of*this;
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an implementation may return all allocated memory[.](#11.sentence-1)
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[249)](#footnote-249)[249)](#footnoteref-249)
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This default constructor is essential,
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since arrays ofvalarray can be useful[.](#footnote-249.sentence-1)
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After initialization, the length of an empty array can be increased with theresize member function[.](#footnote-249.sentence-2)
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[250)](#footnote-250)[250)](#footnoteref-250)
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This constructor is the
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preferred method for converting a C array to avalarray object[.](#footnote-250.sentence-1)
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[251)](#footnote-251)[251)](#footnoteref-251)
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This copy constructor creates
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a distinct array rather than an alias[.](#footnote-251.sentence-1)
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Implementations in which arrays share storage are permitted, but they
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would need to implement a copy-on-reference mechanism to ensure that arrays are
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conceptually distinct[.](#footnote-251.sentence-2)
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