2016. szeptember 12., hétfő 7:28:26 UTC+2 időpontban davidmi...@gmail.com a
következőt írta:
>
> *I have two Golang questions that I hope someone could help me out with.*
>
>
> *1) Am I misunderstanding Golang maps?*
>
>
> *I'm trying to translate a project from PHP to Golang for the websockets
> and the concurrency. *
>
>
> *However, I can't do this.....*
>
>
> * var MyArray [string]string*
>
>
> *Instead, I have to do this.....*
>
>
> * var MyMap map[string]string*
>
>
> *However, since the same array (map) would be used at least once for each
> call to the Golang code from the Front End, which occurs any time a user
> sends data to the Back End, I have been led to believe that I would have to
> lock and unlock the map for each use. Wouldn't that essentially break
> concurrency (or at least eliminate its benefits??? No other user's function
> could use this map until the current user's function is done with it. I'd
> be back to "single threaded" again (concurrently speaking). This would
> defeat much of the point in my switching the project from PHP to Golang. To
> maintain concurrency without blocking other users, one would have to avoid
> using maps. Arrays (maps) are central to programming. How does anyone get
> by in Golang without using Maps?????*
>
>
> *For example, if I do the following.....*
>
>
> *func MyFunc (whatever) *map[string]string *{*
>
>
> var MyMap map[string]string
>
>
> * // Do something with the map*
>
>
> * return MyMap*
>
>
> *}*
>
>
> *func CallingFunction (whatever) {*
>
>
> * MyReturnedMap := go MyFunc(whatever)*
>
>
> *}*
>
>
> *.....would I have to lock and unlock the map or are two separate
> instances of the map declared?*
>
>
> *Again, am** I misunderstanding Golang maps?*
>
>
>
Use the lock for as short time as possible: only around get and set access!
Maybe even:
mMu.RLock()
v, ok := m[k]
mMu.RUnlock()
if ok {...
if v ...
mMu.Lock()
m[k] = v
mMu.Unlock()
By the way your example does not use the map concurrently, as *MyFunc* will
return a new map.
And your code won't even compile! (no "v := go f()" syntax in go).
> *2) Also, how would one build a multidimensional array with a string index
> (or even a map of maps) for something like a large file directory where the
> number of files, folders and levels are unknown at the outset (without
> repeatedly using the append function that apparently uses memory on an
> exponential scale of 2^x)? I've figured out how to do
> map[string]map[string]map[string]string, but one would have to know how
> many levels there would be, in advance, to be able to use something like
> that. Also, when I've tried that, I can't put a string on any level except
> for the last one, since the only data type that any level other than the
> last one will accept is another map! What if the map turns out to be only
> three levels deep for one path and five levels deep for another path?** I've
> tried the following, which I found online, but I can't dynamically add any
> new folders to the directory with any kind of ease. It seems that
> initializing the struct is the only way to get data into the struct without
> declaring a new struct for every manipulation!*
>
>
> *(Below code from
> **http://stackoverflow.com/questions/19080116/golang-tree-like-solution-for-filesystem
>
> <http://stackoverflow.com/questions/19080116/golang-tree-like-solution-for-filesystem>)*
>
>
> package Websocket
>
> import "fmt"
>
> type File struct {
> Name string
> }
>
> type Folder struct {
> Name string
> Files []File
> Folders []Folder
> }
>
> func main() {
> root := Folder{
> Name: "Root",
> Files: []File{
> {"One"},
> {"Two"},
> },
> Folders: []Folder{
> {
> Name: "Empty",
> },
> },
> }
> fmt.Printf("Root %#v\n", root)
> }
>
>
> *Given the above, how would i now add another folder to the directory tree.
> Among many other variations, I've tried the following.....*
>
>
> *root.Folders[0].Name = "MyFirstFolder"*
>
>
> *.....but nothing I have tried has worked.*
>
>
> *What I've been trying to do is set up an array that looks like the
> following.....*
>
>
> *MyArray["Number of Sub Items"] = 6*
>
> *MyArray["Type of Sub Items"] = "Folders"*
>
> *MyArray[0] = "Folder 1"*
>
> *MyArray[1]** = "Folder 2"*
>
> *MyArray[2]** = "Folder 3"*
>
> *MyArray[3]** = "Folder 4"*
>
> *MyArray[4]** = "Folder 5"*
>
> *MyArray[6]** = "Folder 6"*
>
>
> *MyArray[3]**["Number of Sub Items"]** = 3*
>
> *MyArray["Type of Sub Items"] = "Folders"*
>
> *MyArray[3][0] = "Folder 1"*
>
> *MyArray[3][1]** = "Folder 2"*
>
> *MyArray[3][2]** = "Folder 3"*
>
>
> *Note that this problem is not exclusive to directory structure. Using
> directory structure is just a simple way to describe the problem I'm having.*
>
>
> *Alternatively**, are there any libraries that can do the above so that I
> don't have to "reinvent the wheel"?*
>
>
>
For not reinventing the wheel, take a look at http.File, FileSystem, and
Dir.
For using a map: why not use the path (with / as separator) as the key?
Or implement a tree with pointers, if you really need it.
What are you wishing to accompish?
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