[英]Can I in-place construct in Rust?
I like emplace()
ing in C++ which allows to save on move construction and destruction: eg strings.push_back("abcd"s)
means我喜欢 C++ 中的 emplace emplace()
ing,它可以节省移动构造和破坏:例如strings.push_back("abcd"s)
意味着
construct, move, destruct the temporary建造、移动、破坏临时物
while strings.emplace_back("abcd")
is just "construct".而strings.emplace_back("abcd")
只是“构造”。
Can anything similar be achieved in Rust (maybe with compiler optimizations)?可以在 Rust 中实现类似的东西吗(也许通过编译器优化)? The usual vec.push(String::from("abcd"))
seems like (in C)通常的vec.push(String::from("abcd"))
看起来像(在 C 中)
construct + memcpy()构造 + 内存复制()
I'm also interested in cases which are more complex than just pushing strings into a vector.我也对比将字符串推入向量更复杂的情况感兴趣。
I think emplace
feature mostly backed by placement-new feature in C++ and similar unstable feature was removed couple years ago from Rust. Therefore no, it is not possible do the similar with high-level code.我认为emplace
功能主要由 C++ 中的placement-new功能支持,几年前从 Rust 中删除了类似的不稳定功能。因此,不,不可能用高级代码做类似的事情。
Nevertheless you are still able to use ptr::write
and achieve the same behavior in unsafe code.尽管如此,您仍然可以使用ptr::write
并在不安全代码中实现相同的行为。
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