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cppdraft/variant/status.md

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+[variant.status]
+
+# 22 General utilities library [[utilities]](./#utilities)
+
+## 22.6 Variants [[variant]](variant#status)
+
+### 22.6.3 Class template variant [[variant.variant]](variant.variant#variant.status)
+
+#### 22.6.3.6 Value status [variant.status]
+
+[🔗](#lib:valueless_by_exception,variant)
+
+`constexpr bool valueless_by_exception() const noexcept;
+`
+
+[1](#1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L6368)
+
+*Effects*: Returns false if and only if the variant holds a value[.](#1.sentence-1)
+
+[2](#2)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L6372)
+
+[*Note [1](#note-1)*:
+
+It is possible for a variant to hold no value
+if an exception is thrown during a
+type-changing assignment or emplacement[.](#2.sentence-1)
+
+The latter means that even avariant<float, int> can become valueless_by_exception(), for
+instance bystruct S { operator int() { throw 42; }};
+variant<float, int> v{12.f};
+v.emplace<1>(S());
+
+— *end note*]
+
+[🔗](#lib:index,variant)
+
+`constexpr size_t index() const noexcept;
+`
+
+[3](#3)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L6393)
+
+*Effects*: If valueless_by_exception() is true, returns variant_npos[.](#3.sentence-1)
+
+Otherwise, returns the zero-based index of the alternative of the contained value[.](#3.sentence-2)