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fixed defaulted moves on older compilers

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Andrzej Krzemienski committed 2017-11-07 23:34:41 +01:00
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commit 7541076cf1
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doc/1A_on_performance.qbk
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@@ -19,7 +19,7 @@ Lifetime of the `T` inside `_storage` is manually controlled with placement-`new
T _storage;
};
We call it a ['direct] storage. This makes `optional<T>` a trivially-copyable type for scalar `T`s. This only works for compilers that support defaulted functions. On compilers without defaulted functions we still use the direct storage, but `optional<T>` is no longer recognized as trivially-copyable. Apart from scalar types, we leave the programmer a way of customizing her type, so that it is reconized by `optional` as candidate for optimized storage, by specializing type trait `boost::opitonal_config::optional_uses_direct_storage_for`:
We call it a ['direct] storage. This makes `optional<T>` a trivially-copyable type for scalar `T`s. This only works for compilers that support defaulted functions (including defaulted move assignment and constructor). On compilers without defaulted functions we still use the direct storage, but `optional<T>` is no longer recognized as trivially-copyable. Apart from scalar types, we leave the programmer a way of customizing her type, so that it is reconized by `optional` as candidate for optimized storage, by specializing type trait `boost::opitonal_config::optional_uses_direct_storage_for`:
struct X // not trivial
{