I’ve the following code which require multiple packages in cmd package
PATH_SEP = string(os.PathSeparator)
my project structure is like following
go/src/my proj
-cmd
--runners
--otherpackage
-- package2
-- constants
--….
in constants i put the code
PATH_SEP = string(os.PathSeparator)
const2 etc
and in runners and package2/3 etc I use this constant.
is it OK ? otherwise I need to duplicate the code for other packages .
I would suggest to declare struct with constant fields and import that struct in any package you wants to use the constants.
package cmd
type Constants struct{
const1 int
const2 int
}
It would be better to have a separate file for constants. Create a file called global.go which contains all constant structs to be used in different packages that way your code would be cleaner.
Note: We require constants to be shared in multiple files, so it will be better to import the package containing constants. Rather than package containing methods and other details even if we do not need them.
You can use the constants as you describe, there is nothing wrong with it. But it is less intuitive.
How i would go about this is having a root package constants and those can be used anywhere in the project.
go/src/my proj
-cmd
-constants
--runners
--otherpackage
--package2
--….
Related
I need to call multiple constants found in another go project, already run the command
go install
and create the executable but I don't know how to import it into the project where I need it
You're going to want to read up on go modules pretty extensively - they're used everywhere in the go environment nowadays, and a very important concept to grasp.
Once you feel comfortable with that, if this code you speak of is not in module form yet, you'll need to make it that way. After that, the constants you need will need to be exported (i.e capitalized variable names) like this:
package mymath
// unexported variable - local scope only
var pi = 3.14159265
// exported variable - global scope when in a module
var Pi = 3.14159265
Now, you can call mymath.Pi to get that constant value.
go get project-github-or-smthelse-which-routes-to-source-code
I am developing a go package, which is a little bit complex and thus I want to organize the source code into multiple directories.
However, I don't want the users of the package to have to use too long imports. Anyways, the internal structure of the package isn't their concern.
Thus, my package structure looks so:
subDir1
subSubDir1
subSubDir2
subDir2
subSubDir3
...and so on. All of them have their exported calls.
I would like to avoid that my users have to import
import (
"mypackage/subDir1"
"mypackage/subDir1/subSubDir2"
)
...and so on.
I only want, if they want to use an exported function from my package, they should have access all of them by simply importing mypackage.
I tried that I declare package mypackage in all of the .go files. Thus, I had source files in different directories, but with the same package declaration.
In this case, the problem what I've confronted was that I simply couldn't import multiple directories from the same package. It said:
./src1.go:6:15: error: redefinition of ‘mypackage’
"mypackage/mysubdir1"
^
./src1.go:4:10: note: previous definition of ‘mypackage’ was here
"mypackage"
^
./src1.go:5:15: error: redefinition of ‘mypackage’
"mypackage/mysubdir2"
^
./src1.go:4:10: note: previous definition of ‘mypackage’ was here
"mypackage"
^
Is it somehow possible?
You should not do this in any case, as the language spec allows a compiler implementation to reject such constructs. Quoting from Spec: Package clause:
A set of files sharing the same PackageName form the implementation of a package. An implementation may require that all source files for a package inhabit the same directory.
Instead "structure" your file names to mimic the folder structure; e.g. instead of files of
foo/foo1.go
foo/bar/bar1.go
foo/bar/bar2.go
You could simply use:
foo/foo1.go
foo/bar-bar1.go
foo/bar-bar2.go
Also if your package is so big that you would need multiple folders to even "host" the files of the package implementation, you should really consider not implementing it as a single package, but break it into multiple packages.
Also note that Go 1.5 introduced internal packages. If you create a special internal subfolder inside your package folder, you may create any number of subpackages inside that (even using multiple levels). Your package will be able to import and use them (or to be more precise all packages rooted at your package folder), but no one else outside will be able to do so, it would be a compile time error.
E.g. you may create a foo package, have a foo/foo.go file, and foo/internal/bar package. foo will be able to import foo/internal/bar, but e.g. boo won't. Also foo/baz will also be able to import and use foo/internal/bar because it's rooted at foo/.
So you may use internal packages to break down your big package into smaller ones, effectively grouping your source files into multiple folders. Only thing you have to pay attention to is to put everything your package wants to export into the package and not into the internal packages (as those are not importable / visible from the "outside").
Inside your package source code, you have to differentiate your source directories by renamed imports. You can declare the same package mypackage in all of your source files (even if they are in different directories).
However, while you import them, you should give an induvidual names to the directories. In your source src1.go, import the other directories on this way:
import (
"mypackage"
submodule1 "mypackage/mySubDir"
)
And you will be able to reach the API defined in "mypackage" as mypackage.AnyThing(), and the API defined in mySubDir as submodule1.AnyThing().
The external world (i.e. the users of your package) will see all exported entities in myPackage.AnyThing().
Avoid namespace collisions. And use better understable, intuitive naming as in the example.
Yes, this is doable without any problems, just invoke the Go compiler by hand, that is not via the go tool.
But the best advice is: Don't do that. It's ugly and unnecessarily complicated. Just design your package properly.
Addendum (because the real intention of this answer seems to get lost sometimes, maybe because irony is too subtle): Don't do that!! This is an incredible stupid idea! Stop fighting the tools! Everybody will rightfully hate you if you do that! Nobody will understand your code or be able to compile it! Just because something is doable in theory doesn't mean this is a sensible idea in any way. Not even for "learning purpose"! You probably even don't know how to invoke the Go compiler by hand and if you figure it out it will be a major pita.
I have a short program in Go with the following files part of it.
Program directory structure:
myprogram/
main.go
server.go
routines.go
structs.go
These different files contain different function. The structs.go file contains a list of structure type defined, and used in several files of my program. What I want to do, now is to split my program into package like in this example :
main/
main.go // the main program
server/
server.go // a package imported in main
routines/
routines.go // a package imported in main
My problem, is that I do not know where to put structs.go because it contains structures used in several package, as in the 'main.go' code.
How to share efficiently this structs.go file ? Should I include it (via a symlink to the file) in each of the package I defined, i.e serverand routines and also in main ?
My method may be awkward because I'm a beginner in Go, and in programming generally.
Don't link files across packages, that's bad practice. For one, the code will be duplicated. For another, identifiers will be duplicated meaning to denote the same entities (e.g. type or function), but they will be distinct. E.g. if linked and structs.go would contain a type Response definition, you would have 2 distinct types server.Response and routines.Response giving just more confusion.
One solution would be to put structs.go into its own package, e.g. model, and all other packages relying on it can import it (e.g. your main, server and routines).
In a theoretical example: if package A imports package B and structs.go would be needed in both, then it could also be added to package B. If there would be a package C needing only structs.go, then again it would be wiser to create its own package model (so package C doesn't need to import / know about package B, only the new model package).
Also if noone else will use your package and it is not too complex, it might not worth the hassle to organize it into multiple packages.
It is possible to define a type in one package only and to use it in other packages this way:
package one
type A struct{ B int }
Variant 1:
package two
. import "one"
var name A
Variant 2:
package two
import "one"
type A = one.A
var name A
I would prefer variant 2.
I have some questions on package naming for external Go libraries.
I am interested if using generic names like "text" is considered a good practice? Having in mind that I cannot declare a "nested package" and that the library I am building deals with text processing, is it ok to have the package named "text" or should I stick to the library name as a package name too?
I am building a set of libraries (different projects) and I want to combine them under the same package. Is this also problematic? I am new to the Go community and am still not sure if package pollution is a problem or not (I do not see a problem as long as I import few packages in my code).
The reference on that naming topic is "blog: Package names"
It includes:
Avoid unnecessary package name collisions.
While packages in different directories may have the same name, packages that are frequently used together should have distinct names. This reduces confusion and the need for local renaming in client code. For the same reason, avoid using the same name as popular standard packages like io or http.
Check also your package publishing practice, as it will help disambiguate your "text" package from others.
As illustrated in "An Introduction to Programming in Go / Packages":
math is the name of a package that is part of Go's standard distribution, but since Go packages can be hierarchical we are safe to use the same name for our package. (The real math package is just math, ours is golang-book/chapter11/math)
When we import our math library we use its full name (import "golang-book/chapter11/math"), but inside of the math.go file we only use the last part of the name (package math).
We also only use the short name math when we reference functions from our library. If we wanted to use both libraries in the same program Go allows us to use an alias:
import m "golang-book/chapter11/math"
func main() {
xs := []float64{1,2,3,4}
avg := m.Average(xs)
fmt.Println(avg)
}
m is the alias.
As mentioned in the comments by elithrar, Dave Cheney has some additional tips:
In other languages it is quite common to ensure your package has a unique namespace by prefixing it with your company name, say com.sun.misc.Unsafe.
If everyone only writes packages corresponding to domains that they control, then there is little possibility of a collision.
In Go, the convention is to include the location of the source code in the package’s import path, ie
$GOPATH/src/github.com/golang/glog
This is not required by the language, it is just a feature of go get.
Assume there is a function F in package A that some code I'm creating needs to call. How do I call it?
If I'm Calling it from outside package A, then I uses A.F(...) and if I'm inside A I uses F(...). But what if Murphy prevents me from knowing which is true or requires a byte identical line work in both?
[note: I'm taking it as a given that such a case will occur because, in my experience and observations, that is generally a safe assumption. Even in the absence of technical reasons for it, PHBs and legislators are good sources of the ridiculous.]
There is no such syntax. Observe the following things:
Cyclical imports are forbidden. This especially means that a package cannot import itself. Thus, a package cannot refer to one of its symbols S with the pkg.S syntax because it will not be able to import itself.
Even if you solved that problem, observe that packages can be given an arbitrary name once imported. For instance, you could do:
import bar "foo"
Which imports S from package "foo" as bar.S as opposed to the expected foo.S.
The following things could be used to work around this:
In the package "foo", create an internal object foo whose members are the symbols foo exports. This allows you to use the foo.S syntax in foo itself, but is a horrible kludge.
Use an import declaration like
import . "foo"
which allows you to use symbol S from package "foo" as S, i. e. without prefix. Notice that this kind of import declaration, called dot imports, is considered bad style and might break things if the set of symbols you declare / the package you import declares changes.