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| 1 |
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#### Overview <a id="range.as.const.overview">[[range.as.const.overview]]</a>
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`as_const_view` presents a view of an underlying sequence as constant.
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That is, the elements of an `as_const_view` cannot be modified.
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The name `views::as_const` denotes a range adaptor object
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[[range.adaptor.object]]. Let `E` be an expression, let `T` be
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`decltype((E))`, and let `U` be `remove_cvref_t<T>`. The expression
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`views::as_const(E)` is expression-equivalent to:
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- If `views::all_t<T>` models `constant_range`, then `views::all(E)`.
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- Otherwise, if `U` denotes `empty_view<X>` for some type `X`, then
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`auto(views::empty<const X>)`.
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- Otherwise, if `U` denotes `span<X, Extent>` for some type `X` and some
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extent `Extent`, then `span<const X, Extent>(E)`.
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- Otherwise, if `U` denotes `ref_view<X>` for some type `X` and
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`const X` models `constant_range`, then
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`ref_view(static_cast<const X&>(E.base()))`.
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- Otherwise, if `E` is an lvalue, `const U` models `constant_range`, and
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`U` does not model `view`, then `ref_view(static_cast<const U&>(E))`.
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- Otherwise, `as_const_view(E)`.
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[*Example 1*:
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``` cpp
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template<constant_range R>
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void cant_touch_this(R&&);
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vector<char> hammer = {'m', 'c'};
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span<char> beat = hammer;
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cant_touch_this(views::as_const(beat)); // will not modify the elements of hammer
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```
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— *end example*]
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