spec: type identity section not fully updated for 1.9

[jiaweizhang]

The Type identity (link) section of the doc has the following:

these types are identical:

A0, A1, and []string
A2 and struct{ a, b int }
A3 and int
A4, func(int, float64) *[]string, and A5

B0, B0, and C0
[]int and []int
struct{ a, b *T5 } and struct{ a, b *T5 }
func(x int, y float64) *[]string, func(int, float64) (result *[]string), and A5

B0 and B1 are different because they are new types created by distinct type definitions; func(int, float64) *B0 and func(x int, y float64) *[]string are different because B0 is different from []string.

Suggested fix

these types are identical:

A0, A1, and []string
A2, struct{ a, b int }
A3 and int
A4, func(A3, float64) *A0, func(x int, y float64) *[]string, func(int, float64) *[]string, and A5
B0 and C0

B0 and B1 are different because they are new types created by distinct type definitions. Similarly, func(int, float64) *B0 and func(x int, y float64) *A1 are different because B0 and A1 are created by distinct type definitions (A1 is an alias of []string while B0 is a new, distinct type with the same underlying type as []string.

Rationale

This section of the docs was not completely updated to reflect the addition of alias declarations. I also recommend moving the "Properties of types and values" section containing "Type identity" down under the "Declarations" (specifically "Type declarations"), so the concept of alias declarations is introduced before they are used.

[griesemer]

I don't see any issues here:

• struct{a, b int} and struct{a, c int} are clearly different as they have different field names.
• Yes B0 and C0 are identical but the list is meant to be exemplary, not exhaustive. Otherwise we'd have to add much more. What we have is correct.

Regarding ordering: It's difficult to come up with the "best order" in a language spec that is naturally recursive. Thanks for the suggestion, but for now I prefer leaving it as is, because a) there's hyperlinks that make it easy to jump around, and b) people got used to the current order.

Closing.

[jiaweizhang]

The changes I made were more concerning the lines I took out:

[]int and []int
struct{ a, b *T5 } and struct{ a, b *T5 }

What exactly is the purpose of these two lines?

[griesemer]

See #9226 for a discussion.

[gopherbot]

Change https://golang.org/cl/87417 mentions this issue: spec: remove example explaining that type B0 and B0 are identical