From 06cb303d807d85766c62085a0095d17798be679c Mon Sep 17 00:00:00 2001 From: dbarobin Date: Fri, 7 Aug 2015 10:54:12 +0800 Subject: [PATCH] [Bug] Fix wrong contents of 8.4 and add sample code --- eBook/08.4.md | 6 +++--- eBook/examples/chapter_8/maps_forrange2.go | 21 +++++++++++++++++++++ 2 files changed, 24 insertions(+), 3 deletions(-) create mode 100644 eBook/examples/chapter_8/maps_forrange2.go diff --git a/eBook/08.4.md b/eBook/08.4.md index 2b03e11..e4e9bba 100644 --- a/eBook/08.4.md +++ b/eBook/08.4.md @@ -1,8 +1,8 @@ -# 8.3 map 类型的切片 +# 8.4 map 类型的切片 -假设我们想获取一个 map 类型的切片，我们必须使用两次 `make()` 函数，第一次分配切片，第二次分配 切片中每个 map 元素（参见下面的例子 8.3）。 +假设我们想获取一个 map 类型的切片，我们必须使用两次 `make()` 函数，第一次分配切片，第二次分配 切片中每个 map 元素（参见下面的例子 8.4）。 -示例 8.3 [maps_forrange.go](examples/chapter_8/maps_forrange.go)： +示例 8.4 [maps_forrange2.go](examples/chapter_8/maps_forrange2.go)： ```go package main diff --git a/eBook/examples/chapter_8/maps_forrange2.go b/eBook/examples/chapter_8/maps_forrange2.go new file mode 100644 index 0000000..f86bbd7 --- /dev/null +++ b/eBook/examples/chapter_8/maps_forrange2.go @@ -0,0 +1,21 @@ +package main + +import "fmt" + +func main() { + // Version A: + items := make([]map[int]int, 5) + for i := range items { + items[i] = make(map[int]int, 1) + items[i][1] = 2 + } + fmt.Printf("Version A: Value of items: %v\n", items) + + // Version B: NOT GOOD! + items2 := make([]map[int]int, 5) + for _, item := range items2 { + item = make(map[int]int, 1) // item is only a copy of the slice element. + item[1] = 2 // This 'item' will be lost on the next iteration. + } + fmt.Printf("Version B: Value of items: %v\n", items2) +}