request switch statement with common block

[MattCoder]

On Sunday, 4 August 2013 at 16:16:25 UTC, Andre Artus wrote:
> On Sunday, 4 August 2013 at 15:57:32 UTC, Andre Artus wrote:
>> On Sunday, 4 August 2013 at 10:14:50 UTC, Kagamin wrote:
>>> On Saturday, 3 August 2013 at 18:56:47 UTC, JS wrote:
>>>> Um, it can actually save a lot of type and errors.
>>>>
>>>> having two places to change is very error prone.
>>>>
>>>> if (cond) { }
>>>> switch(cond)
>>>
>>> What is error-prone is evaluation of a complex condition 
>>> twice assuming it will result in the same value. That's also 
>>> a common error with C macros. You should save the value in a 
>>> variable:
>>>
>>> auto cond = complexCond;
>>> if (cond) { }
>>> switch(cond)...
>>
>> There is also a subtle, but in my opinion important, 
>> distinction between the expressions accepted by 'if' and 
>> 'switch'.
>>
>> With 'if' the expression must evaluate to boolean, whereas 
>> with 'switch' the expression evaluates to an integral or 
>> {w|d}char[] type. With a 'switch' the condition is completed 
>> in the 'case'.
>
> Oops. I think I hit spacebar twice and the message was posted 
> before I finished it.
>
> Taking an example from the D language reference,
>
>>
>> int number;
>> string message;
>> switch (number)
>> {
>> 	default: // valid: ends with 'throw'
>> 	throw new Exception("unknown number");
>> 	case 3:
>> 		message ~= "three "; break;
>> 	case 4:
>> 		message ~= "four "; continue;
>> 	case 5:
>> 		message ~= "five "; goto case;
>> 	case 6:
>> 		message ~= "six "; break;
>> 	case 1:
>> 	case 2:
>> 		message = "one or two";
>> }
>
> With the inclusion of 'default' the condition covers the whole 
> range of 'int'. The programmer may only want the pre  and post 
> code to be executed for every other case (1..6).


Like I said, it would be nice if we could extend some D features 
without change the compiler source, maybe like macros in LISP.

The switch statement should have an event handler like: 
onBeforeMatch or onAfterMatch to handle this.

But for what I saw on this thread, this is only possible changing 
the compiler source. :/

Matheus.