获取结构元素的静态类型

Question

I've looked in the Golang documentation and haven't seen an example of how to achieve what I'm looking to do. Specifically, I'm trying to write a map from inodes, represented by syscall.Stat_t.Ino, which has type uint64 on my machine, to ino_entry, defined as

type ino_entry struct {
    st    *syscall.Stat_t
    nodes []string
}

where nodes represents the names of all the files hard linked to the inode.

However, I want to avoid putting the literal type uint64 in the specification of the map if I can. That is, instead of writing map [uint64] ino_entry, I'd prefer to write map [typeof(syscall.Stat_t.Ino)] ino_entry, where typeof(x) returns the static (i.e., compile-time) type of x. I've tried map [syscall.Stat_t.Ino] ino_entry and, by analogy with type switches, map [syscall.Stat_t.Ino.(type)] ino_entry, but both of these are syntax errors. Needless to say, map [reflect.Typeof(syscall.Stat_t.Ino)] ino_entry doesn't work. As far as I can tell, the only way to implement this without hardcoding the type of the structure element is to use inomap := make(map [interface{}] ino_entry) and then access the elements using type assertions (I don't know the correct syntax for this though).

Is there a way to declare the type of a variable based on the static type of another variable, or struct or interface member, without hardcoding that type explicitly?

Answer 1

It looks like you are trying to use Reflection to ensure machine portability. If that is the case there is a better tool you can use.

go build can handle conditional file inclusion for a build based on arch and os.

So create some files for each arch and os combination you support. At the top of each file add some build constraints.

// +build linux,386 for instance will cause the go command to only use this file on linux machines with a 386 arch.

Then in that file add a type alias for the type that fits that arch: type Ino uint64

Finally create your map as a map[Ino]ino_entry.

Wala! machine portability using type aliasing and conditional file inclusion for go.

You can read more about go's build constraints here: http://golang.org/pkg/go/build/