Throwing exception in constructor

[Vijay Nayar]

On Tue, 16 Aug 2011 19:33:06 +0200, Timon Gehr wrote:

> On 08/16/2011 07:08 PM, Stijn Herreman wrote:
>> Why is the return statement required, while nothing after the Exception
>> is executed?
>> Error: one path skips constructor
>>
>> public this(string p1, string p2, string p3) {
>> string json = download_string(...);
>>
>> if (json is null)
>> {
>> throw new Exception("404");
>> writeln("test");
>> return;
>> }
>> else
>> {
>> this(json);
>> }
>> }
>>
>> package this(string json)
>> {
>> ...
>> }
> 
> The Exception has no influence, the following code will still get the
> error:
> 
> class JSON{
>      public this(string p1, string p2, string p3) {
>          string json = download_string(...);
> 
>          if (json is null)
>          {
>              ...
>          }
>          else
>          {
>              this(json);
>          }
>      }
> 
>      this(string json)
>      {
>          ...
>      }
> }
> 
> This is afaik by design (described somewhere in TDPL). The idea is that
> a constructor can either construct the value itself in all code paths or
> delegate construction to another constructor in all code paths. The fact
> that the code compiles with return but not with throw is probably a bug.


Well I'll be a monkey's uncle.  I tried it out and sure enough you are 
correct.  I'm still reading TDPL, and now I'm curious to find the 
rationale.

   public this(string value) {
        if (value == "Hambo") {
            _value = 999;
        } else {
            this(to!int(value));
        }
    }