英文:
map of map of structs and "assignment to entry in nil map"
问题
这里有一个例子，每次都会出现assignment to entry in nil map的错误：
https://play.golang.org/p/LudJs0rVbs
为了演示我想要做的事情，这里有一个简单的版本，它会导致对数据库进行两次查找（你需要在第11行使用你的想象力）：
https://play.golang.org/p/YZNFeMHyMs
基本上，我想要做的是：
things := make(map[string]map[string][]Struct)
...
stuff, there := things["first key"]
if !there {
things["first key"] = getAMapOfStringToStructs()
}
doSomethingWith(things["first key"])
我已经查看了更多关于maps-of-maps的简单示例，但似乎无法将其应用到我的问题上。
英文:
Here's an example where I get assignment to entry in nil map every time:
https://play.golang.org/p/LudJs0rVbs
To demonstrate what I'm trying to do, here's a naive version that causes 2 lookups to the database (you'll have to use your imagination on line 11):
https://play.golang.org/p/YZNFeMHyMs
Basically, I'm trying to do this:
things := make(map[string]map[string][]Struct)
...
stuff, there := things["first key"]
if !there {
things["first key"] = getAMapOfStringToStructs()
}
doSomethingWith(things["first key"])
I've looked at the more trivial examples of maps-of-maps here but I can't seem to map that to my problem.
答案1
得分: 2
你从未在allEntries映射上执行过make操作：
allEntries = make(map[string]map[string][]Thing)
https://play.golang.org/p/ecdUU30FQT
英文:
You never did make on your allEntries map:
allEntries = make(map[string]map[string][]Thing)
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