CaseStatement specification issue

[AsmMan via Digitalmars-d]

On Thursday, 14 August 2014 at 16:01:05 UTC, Baz wrote:
> On Thursday, 14 August 2014 at 13:19:36 UTC, Sergey Kozyr wrote:
>> Sorry for previous message. Once again:
>>
>> I was reading D language reference and found some issue with
>> "case ... :" statement specifications.
>> Documentation http://dlang.org/statement#CaseStatement  says
>> that after
>>
>> case 1:
>>
>> must be non-empty statement "ScopeStatementList". For example
>>
>> case 1:
>>  return true;
>>
>> case 2: {
>> }
>>
>> case 3: ;
>>
>> But next example concerns me:
>>
>> case 1:
>> case 2:
>>  return true;
>> case 3:
>>  return false;
>>
>> After "case 1:" we see no statement at all. This conflicts 
>> with "CaseStatement" rule of documentation. But this is right 
>> D code.
>> I think language reference must be updated.
>
> It's a "fall trough":
>
> https://en.wikipedia.org/wiki/Switch_statement#Fallthrough

It's a fall trough but it is not the reason why it does works. It 
does because (as Daniel already mentioned) a case is a valid 
statement, therefore a case following other case is a totally 
valid statement.

for example:

case 1:
case 2:
   return true;

There are three statements. One which must be followed by another 
(case keyword) and another by an expression (return keyword).

It is not even a special-case in the switch in C language. The 
switch keyword accept a expression constant as argument and must 
be followed by a statement, so:

switch(1) return 0;

is valid C code and no standard-compliant compiler must give an 
error about that. The fact we can do:

switch(E)
{
    case 1: ... break;
    case 2: .... break;
default: ... break;
}

That's why compound-statement is a statement too (which switch 
does accept same reason why break keyword is needed)