geno

geno

Geno is a golang tool to help generate generic package from an annotated package. It's goal is to experiment/reproduce the idea of generic pacakge developped in this topic

How does it work?

The most important component is an annotated package. It is made by adding a tag 'gen:N' in the comment section of an interface declaration. You should first alias the empty interface, or any other interface you want to specialize. eg:

type Data interface{}  // <gen:1>

The new alias must be used consistently across your package. If you need more than one specialized type, you can list them like this:

type Key interface{}  // <gen:1>
type Value interface{} // <gen:2>

Generating

Once you have an annotated package, you can generate specialized version with the geno tool. Geno will create a new package by replacing all instance of the annotated types with the one given in parameter. The command

geno -package="champioj/geno/example/list/intlist" -types="int"

will create a new package named intlist with every instance of the type annotated with 'gen:1' replaced with the int type. By convention, the name of the package is the base of the path and must be a subdirectory of the package you want to specialize. Multiple spesialized type are separated by a comma:

geno -package="champioj/geno/example/list/intlist" -types="int,string"

It is possible to use types defined in other package. For example a list of list of int would be:

geno -package="champioj/geno/example/list/intofIntlist" -types="champioj/geno/example/list/intlist.List"

Import will be automatically added ... but beware of cyclic dependency!

Autogeneration

It's possible to add annotation to import so a single call to geno is able to generate every specialized package you need. Add the import as if the package were already created. Then annotate it with its specialization:

import(
    "champioj/geno/example/list/intlist" // <gen:int>
    "champioj/geno/example/list/intofIntlist" // <gen:champioj/geno/example/list/intlist.List>
)

You can observe that it mimic the parameters -package and -types from the geno tool. Once it done, you can make a single call to geno:

geno -recursive="user/foo/bar"

Geno will parse the package "user/foo/bar" and all it import recursively and automatically generate every specialized type it found.

A word on cyclic dependencies

The main drawback which is inherent to the logic of the program is the problem of cyclic dependencies. It is not possible to declare a type in a package, and use a specialized package which use that type cause it would create a cyclic dependency. If you want to do it, you have to put your type in its own packge. I would gladly receive any idea on how to mitigate or solve this problem.