The release of Go version 1, Go 1 for short, is a major milestone in the development of the language. Go 1 is a stable platform for the growth of programs and projects written in Go.
Go 1 defines two things: first, the specification of the language; and second, the specification of a set of core APIs, the "standard packages" of the Go library. The Go 1 release includes their implementation in the form of two compiler suites (gc and gccgo), and the core libraries themselves.
It is intended that programs written to the Go 1 specification will continue to compile and run correctly, unchanged, over the lifetime of that specification. At some indefinite point, a Go 2 specification may arise, but until that time, Go programs that work today should continue to work even as future "point" releases of Go 1 arise (Go 1.1, Go 1.2, etc.).
Compatibility is at the source level. Binary compatibility for compiled packages is not guaranteed between releases. After a point release, Go source will need to be recompiled to link against the new release.
The APIs may grow, acquiring new packages and features, but not in a way that breaks existing Go 1 code.
Although we expect that the vast majority of programs will maintain this compatibility over time, it is impossible to guarantee that no future change will break any program. This document is an attempt to set expectations for the compatibility of Go 1 software in the future. There are a number of ways in which a program that compiles and runs today may fail to do so after a future point release. They are all unlikely but worth recording.
import . "path", additional names defined in the imported package in future releases may conflict with other names defined in the program. We do not recommend the use of
import .outside of tests, and using it may cause a program to fail to compile in future releases.
Of course, for all of these possibilities, should they arise, we would endeavor whenever feasible to update the specification, compilers, or libraries without affecting existing code.
These same considerations apply to successive point releases. For instance, code that runs under Go 1.2 should be compatible with Go 1.2.1, Go 1.3, Go 1.4, etc., although not necessarily with Go 1.1 since it may use features added only in Go 1.2
Features added between releases, available in the source repository but not part of the numbered binary releases, are under active development. No promise of compatibility is made for software using such features until they have been released.
Finally, although it is not a correctness issue, it is possible that the performance of a program may be affected by changes in the implementation of the compilers or libraries upon which it depends. No guarantee can be made about the performance of a given program between releases.
Although these expectations apply to Go 1 itself, we hope similar considerations would be made for the development of externally developed software based on Go 1.
Code in sub-repositories of the main go tree, such as code.google.com/p/go.net, may be developed under looser compatibility requirements. However, the sub-repositories will be tagged as appropriate to identify versions that are compatible with the Go 1 point releases.
Finally, the Go tool chain (compilers, linkers, build tools, and so on) are under active development and may change behavior. This means, for instance, that scripts that depend on the location and properties of the tools may be broken by a point release.
These caveats aside, we believe that Go 1 will be a firm foundation for the development of Go and its ecosystem.