他们为什么不同

Question

In Golang spec:

type (
    T0 []string
    T1 []string
)

it says T0 and T1 are different because they are named types with distinct declarations.but there is a rule: Two named types are identical if their type names originate in the same TypeSpec. so why T0 and T1 are different?

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EDIT:

in spec it also says:

A type declaration binds an identifier, the type name, to a new type that has the same underlying type as an existing type, and operations defined for the existing type are also defined for the new type. The new type is different from the existing type.

Answer 1

Given:

type (
    T0 []string
    T1 []string
)

The Go Programming Language Specification

Version of June 28, 2017

A type definition creates a new, distinct type with the same underlying type and operations as the given type, and binds an identifier to it.

TypeDef = identifier Type .

The new type is called a defined type. It is different from any other type, including the type it is created from.

A defined type is always different from any other type. Otherwise, two types are identical if their underlying type literals are structurally equivalent; that is, they have the same literal structure and corresponding components have identical types.

T0 and T1 are defined types and are, therefore, different.

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References:

The Go Programming Language Specification

Version of June 28, 2017

Types

A type determines a set of values together with operations and methods specific to those values. A type may be denoted by a type name, if it has one, or specified using a type literal, which composes a type from existing types.

Named instances of the boolean, numeric, and string types are predeclared. Other named types are introduced with type declarations.

Type declarations

A type declaration binds an identifier, the type name, to a type. Type declarations come in two forms: alias declarations and type definitions.

TypeDecl = "type" ( TypeSpec | "(" { TypeSpec ";" } ")" ) .
TypeSpec = AliasDecl | TypeDef .

Alias declarations

An alias declaration binds an identifier to the given type.

AliasDecl = identifier "=" Type .

Within the scope of the identifier, it serves as an alias for the type.

Type definitions

A type definition creates a new, distinct type with the same underlying type and operations as the given type, and binds an identifier to it.

TypeDef = identifier Type .

The new type is called a defined type. It is different from any other type, including the type it is created from.

Type identity

Two types are either identical or different.

A defined type is always different from any other type. Otherwise, two types are identical if their underlying type literals are structurally equivalent; that is, they have the same literal structure and corresponding components have identical types.