// mapextra holds fields that are not present on all maps. type mapextra struct { // 如果 key 和 value 都不包含指针,并且可以被 inline(<=128 字节) // 就使用 hmap的extra字段 来存储 overflow buckets,这样可以避免 GC 扫描整个 map // 然而 bmap.overflow 也是个指针。这时候我们只能把这些 ov...
常见用法 var ages map[string]int // 只声明不初始化是nil,赋值会panic: assignment to entry in nil map fmt.Println(ages == nil) // "true" fmt.Println(len(ages
https://dave.cheney.net/2018/05/29/how-the-go-runtime-implements-maps-efficiently-without-generics#easy-footnote-1-3224 https://github.com/golang/go/blob/master/src/runtime/map.go https://studygolang.com/articles/25134 https://www.linkinstar.wiki/2019/06/03/golang/source-code/graphic-...
我们就带着这些问题,深入地探索一下 Golang 是如何实现 Map 的。 Map 概述 我们知道 Map 有以下几个基本特点: Map 是一个无序的 key/value 集合; Map 中所有的 key 都是不同的; 通过给定的 key ,可以在常数时间复杂度内查找、更新或删除相应的 value。
Go中函数调用只有值传递,但是类型引用有引用类型,他们是:slice、map、channel。来看看官方的说法: There’s a lot of history on that topic. Early on, maps and channels were syntactically pointers and it was impossible to declare or use a non-pointer instance. Also, we struggled with how arrays sh...
A map will be a perfect fit for the above use case use case. The currency code can be the key and the currency name can be the value. Maps are similar to dictionaries in other languages such as Python. How to create a map?
oldbuckets unsafe.Pointer // previous bucket array of half the size, non-nil only when growing nevacuate uintptr // progress counter for evacuation (buckets less than this have been evacuated) extra *mapextra // optional fields } // mapextra holds fields that are not present on all maps....
2. 业务依赖 key 次序时,如何解决随机化问题其实 Go maps in action 一文已经给出了解决方法: If you require a stable iteration order you must maintain a separate data structure that specifies that order. 可见,需要另外维护一个数据结构来保持有序的 key,然后根据有序 key 来遍历 map。
map[KeyType]ValueType KeyType 必须是可比较的类型,可比较类型官方定义的是 boolean、numeric、string、pointer、channel、和 interface types、以及包含这些类型的 structs 或 arrays。不可比较的如 slices、maps 和 functions,用不了==。 map 类型是引用类型,所以直接声明的变量0值是 nil,它并不指向一个初试化的...
为了避免这个问题,需要有个地方能够直接引用这些溢出桶,也就是hmap 的extra字段,该字段为*mapextra类型。 // mapextra holds fields that are not present on all maps. type mapextra struct { // If both key and elem do not contain pointers and are inline, then we mark bucket // type as contain...