Go1point1Gotchas.md

Go 1.1 "gotchas"

While Go 1.1 is compatible with Go 1.0, the compatibility promise permits the Go authors to break existing programs if they were incorrect in the first place.

Here are a few ways in which the bug fixes in Go 1.1 may have broken your Go programs.

Unknown foo.Bar field in struct literal

Struct field names must not include package qualifiers. For example, take this struct with an embedded *bytes.Buffer field:

type S struct {
	*bytes.Buffer
}

In Go 1.0 the compiler would (incorrectly) accept this struct literal:

s := S{
	bytes.Buffer: new(bytes.Buffer),
}

Under Go 1.1 the compiler rejects this. Instead you should use the field name without the package qualifier:

s := S{
	Buffer: new(bytes.Buffer),
}

Initialization loop

The Go 1.1 compiler now better detects initialization loops.

For instance, the following code compiled under Go 1.0.

var funcVar = fn

func fn() {
	funcVar()
}

Such code must now use an init function for the variable assignment to avoid the initialization loop.

var funcVar func()

func fn() {
	funcVar()
}

func init() {
	funcVar = fn
}

In particular, this affects users of App Engine's delay package.

Cannot fallthrough final case in switch

Go 1.0 permitted fallthrough in the final case of a switch statement:

switch {
case false:
	fallthrough // fall through to 'true' case
case true:
	fallthrough // fall through to... nowhere?
}

A language change affecting return requirements led us to make the superfluous fallthrough illegal.

The fix is to remove such statements from your code.

Duplicate argument name in parameters and return values

A compiler bug permitted function type declarations with parameters and return values of the same name. This would compile under Go 1.0:

type T func(a int) (a int)

Under Go 1.1, the compiler gives an error:

	duplicate argument a

The fix is to rename the arguments so that they use different names.

Package "go" forbidden

The import path "go" is now reserved. If you have a package in your workspace whose import path is "go", you will need to rename it and move it somewhere else.

While it was permitted, it is a bad idea to use this import path. The standard library includes "go/parser", "go/ast", and so on. It's posssible that a "go" package might be introduced in a future Go release, making your "go" package unusable.

Please read How to write Go code for more details about import paths.