Go 1.4 (2014-12-10)

Go 1.4 was released in December 2014, focusing on implementation improvements, including garbage collector optimizations and rewriting the runtime in Go (preparing for Go 1.5 bootstrapping). Additionally, it added official support for Android.

Major Changes

Language

• For-range Loop: Previously required for _ = range x, now can be shortened to for range x.

  // Before Go 1.4
  for _ = range ch { ... }
  // Go 1.4 and later
  for range ch { ... }

Toolchain

• Android Support: Go 1.4 can build binaries running on Android ARM processors. With the golang.org/x/mobile library, you can write Android apps.

• Contiguous Stacks: The runtime now uses contiguous stacks. When stack space is insufficient, a larger new stack is allocated and data is copied, rather than linking a new stack segment as before. This eliminates the "hot stack split" performance issue and allows goroutines to start with a smaller stack (2KB).

• Canonical Import Paths: Package declarations can include comments to specify their canonical import path. If a user tries to import the package via another path, the go command will refuse to compile.

  package pdf // import "rsc.io/pdf"

• go generate: Added the go generate subcommand, used to scan for //go:generate directives in source code and execute corresponding commands. This is typically used for code generation (like Stringer methods, Yacc parsers, etc.).

• Internal Packages: Introduced the concept of internal directories. Packages in a directory named internal can only be imported by code in the directory tree rooted at the parent of internal. Although mainly enforced in the main repository in Go 1.4, it laid the foundation for widespread adoption in Go 1.5.

Standard Library

• testing: Supports TestMain function, allowing global setup and teardown before and after test execution.

  func TestMain(m *testing.M) {
      setup()
      code := m.Run()
      teardown()
      os.Exit(code)
  }

• sync/atomic: Added Value type for atomically storing and loading values of any type (often used for configuration loading, etc.).

• syscall: The syscall package is frozen and no new system calls will be added. New system call development has moved to the golang.org/x/sys sub-repository.

References

For more details, please refer to the official release notes: Go 1.4 Release Notes