libphobos/testsuite/libphobos.exceptions/chain.d

   1 // Author: Ali Çehreli
   2 // See https://forum.dlang.org/post/o2n7f8$2p1t$1@digitalmars.com
   3
   4 import core.stdc.stdio;
   5
   6 class TestException : Exception
   7 {
   8     this(string msg)
   9     {
  10         super(typeof(this).stringof~": "~msg);
  11     }
  12 }
  13
  14 class TestError : Error
  15 {
  16     this(string msg)
  17     {
  18         super(typeof(this).stringof~": "~msg);
  19     }
  20 }
  21
  22 // Causes an exception chain where the node at index errorIndex is an
  23 // Error (others are all Exceptions).
  24 void causeExceptionChain(size_t chainLength, size_t errorIndex)
  25 {
  26     void throws(size_t n)
  27     {
  28         scope (exit)
  29         {
  30             string msg = [ cast(char)('a'+n) ].idup;
  31             if (n == errorIndex)
  32             {
  33                 throw new TestError(msg);
  34             }
  35             else
  36             {
  37                 throw new TestException(msg);
  38             }
  39         }
  40
  41         if (n != 0)
  42         {
  43             // Redundant 'return' keyword due to
  44             // https://issues.dlang.org/show_bug.cgi?id=16960
  45             return throws(n - 1);
  46         }
  47     }
  48
  49     throws(chainLength - 1);
  50 }
  51
  52 void main()
  53 {
  54     try
  55     {
  56         // -1 would mean "no Error in the chain". Change this to a
  57         // number between 0 and 4 (inclusive) then you will realize
  58         // that the Exception below will not be caught.
  59         size_t errorIndex = 3;
  60         causeExceptionChain(5, errorIndex);
  61     }
  62     catch (Error original)
  63     {
  64         printf("Caught\n");
  65         string prefix = "";
  66         for ({ size_t i; Throwable ex = original; } ex; ex = ex.next, ++i)
  67         {
  68             printf("%.*s%.*s\n", cast(int)prefix.length, prefix.ptr, cast(int)ex.msg.length, ex.msg.ptr);
  69             prefix = prefix~" ";
  70         }
  71         printf("Bypassed chain was:\n");
  72         prefix = "";
  73         for ({ size_t i; Throwable ex = original.bypassedException; } ex; ex = ex.next, ++i)
  74         {
  75             printf("%.*s%.*s\n", cast(int)prefix.length, prefix.ptr, cast(int)ex.msg.length, ex.msg.ptr);
  76             prefix = prefix~" ";
  77         }
  78     }
  79 }