Throwing exception in constructor

[Stijn Herreman]

On 16/08/2011 19:24, Vijay Nayar wrote:
> On Tue, 16 Aug 2011 19:08:53 +0200, 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)
>> 	{
>> 		...
>> 	}
>
> What compiler are you using?  Using DMD2 (DMD32 D Compiler v2.054), I
> have no problem with the example below.  I suspect the problem may not
> have anything to do with return statements.
>
> import std.stdio;
> import std.conv;
>
> class Hambo {
>      public int _value;
>
>      public this(string value) {
>          this(to!int(value));
>      }
>
>      public this(int value) {
>          if (value<  10) {
>              throw new Exception("Not high enough.");
>          } else {
>              _value = value;
>          }
>      }
> }
>
> void main() {
>      // Throws: object.Exception at constructor.d(13): Not high enough.
>      //Hambo ham1 = new Hambo("4");
>      Hambo ham2 = new Hambo("14");
>      writeln(ham2._value);
> }
It happens only when chaining constructors.

Doesn't compile:
class Hambo {
     public int _value;

     public this(string value) {
		if (value == "") {
			throw new Exception("Empty.");
		} else {
			this(to!int(value));
		}
     }

     public this(int value) {
         if (value < 10) {
             throw new Exception("Not high enough.");
         } else {
             _value = value;
         }
     }
}

Compiles:
class Hambo {
     public int _value;

     public this(string value) {
		if (value == "") {
			throw new Exception("Empty.");
			return;
		} else {
			this(to!int(value));
		}
     }

     public this(int value) {
         if (value < 10) {
             throw new Exception("Not high enough.");
         } else {
             _value = value;
         }
     }
}

Compiles:
class Hambo {
     public int _value;

     public this(string value) {
		if (value == "") {
			throw new Exception("Empty.");
		}
     }

     public this(int value) {
         if (value < 10) {
             throw new Exception("Not high enough.");
         } else {
             _value = value;
         }
     }
}