c++ - The meaning of synonym in typedef -

the following paragraph taken [dcl.typedef]:

within scope of declaration, typedef-name syntactically equivalent keyword , names type associated identifier in way described in clause 8. typedef-name synonym type. typedef-name not introduce new type way class declaration (9.1) or enum declaration does.

the other relevant passage need [dcl.type]

as general rule, @ 1 type-specifier allowed in complete decl-specifier-seq of declaration or in type-specifier-seq or trailing-type-specifier-seq. exceptions rule following: … long can combined long.

in following code, i1 synonym long.

typedef long i1; typedef long i1 i2; 

thus, expect second line understood typedef long long i2. however, msvc2015rc fails with

error c2146 syntax error: missing ';' before identifier 'i2'

can point part of standard invalidates expectation?

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update

my point that, far understand grammar in [dcl.type],

type-specifier:     trailing-type-specifier     class-specifier     enum-specifier trailing-type-specifier:     simple-type-specifier     elaborated-type-specifier     typename-specifier     cv-qualifier type-specifier-seq:     type-specifier attribute-specifier-seq opt     type-specifier type-specifier-seq trailing-type-specifier-seq:     trailing-type-specifier attribute-specifier-seq opt     trailing-type-specifier trailing-type-specifier-seq 

a decl-specifier-seq allow sequence of type specifiers long satisfy combination rules. seems me type not same type-specifier though type specified type specifier ;-)

alright, i'll answer.

first, looking @ this:

a typedef-name syntactically equivalent keyword

this means typedef-names follow syntax of keywords. not mean typedef-name equivalent particular keyword. it's new, unique keyword.

then have,

a typedef-name synonym type.

so, given typedef long i1;, "another type"? long int, not long.

in addition, "type"? @ least, type-specifier not type. type-specifier long represents type "long int" (see table 10 of n3337 or table 9 of n4296).

i'll copy comment here:

i1 synonym type long int. not synonym keyword long. otherwise i1 double , long double.

though perhaps should have said, i1 not synonym type-specifier long, synonym type long int.