英文:
Reflect Type.Field() order
问题
我无法在文档中找到相关信息，是否有保证字段的顺序与结构中声明的顺序相匹配？从逻辑上看，它似乎是符合的（由于内存布局），并且似乎也是按照这种方式执行的，但我只是想确认一下。如果这不是一个保证，我不希望代码以后出现问题。
例如，如果我有以下代码：
type Foo struct {
bar string `tag:"bar"`
baz string `tag:"baz"`
barbaz string `tag:"barbaz"`
}
并且我运行了以下代码：
var c Foo
t := reflect.TypeOf(c)
nf := t.NumField()
tags := make([]string, nf)
for f := 0; f < nf; f++ {
tags[f] = t.Field(f).Tag.Get("tag")
}
tags 是否保证为 ["bar", "baz", "barbaz"]？
英文:
I can't seem to find it in documentation, is there any guarantee that the order from the fields will match the order declared in the struct? I know it seems like it would logically (due to memory layout),and it seems to perform this way too, but just making sure. I don't want code to break later on if this isn't a guarantee.
For example, if I had
type Foo struct {
bar string `tag:"bar"`
baz string `tag:"baz"`
barbaz string `tag:"barbaz"`
}
and I ran this code:
var c Foo
t := reflect.TypeOf(c)
nf := t.NumField()
tags := make([]string, nf)
for f := 0; f < nf; f++ {
tags[f] = t.Field(f).Tag.Get("tag")
}
Would tags be guaranteed to be ["bar", "baz", "barbaz"]?
答案1
得分: 10
我在golang-nuts上询问了这个问题，并从Ian Lance Taylor那里得到了一个回答，确认它是按照声明顺序进行的，并且不会改变。
它是按照结构体声明中字段出现的顺序进行的。
它不会改变。如果你发现有一个情况不是按照声明顺序的，请提交一个bug报告。谢谢。
英文:
I asked on golang-nuts about this, and got an answer from Ian Lance Taylor confirming it's declaration order, and will not change.
> It's the order in which the fields appear in the struct declaration.
It's not going to change. If you find a case where it is not the
order in the declaration, please file a bug. Thanks.
答案2
得分: 7
尽管标准的Go编译器（GC）和GCCGO目前不会重新排序结构体字段，但我不会依赖于任何排序。文档中没有明确的保证。这可能会在将来的版本中完成。
字段重新排序是一种在结构体内部对字段进行内存对齐的技术，而不需要使用填充（不必要地增加结构体的内存表示）。你可以在以下问题中阅读相关内容：
英文:
Even though GC (the standard Go compiler) and GCCGO don't reoder struct fields today, I wouldn't rely on any ordering. There are no express guarantees in the documentation. This might be done in a future version of either compiler.
Field reordering is a technique used to memory-align fields inside of a struct without resorting to padding (unnecessarily inflating the struct's memory representation). You can read about it in the following question:
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