add GDB trick

.gdbinit

@@ -0,0 +1,106 @@
+define rp
+  set $types = rb_type($arg0)
+
+  if $types == 0x01
+    # RUBY_T_OBJECT
+    p "T_OBJECT:"
+    p (struct RBasic *)($arg0)
+  else
+  if $types == 0x02
+    # RUBY_T_CLASS
+    p "T_CLASS:"
+    p (struct RBasic *)($arg0)
+  else
+  if $types == 0x03
+    # RUBY_T_MODULE
+    p "T_MODULE:"
+    p (struct RBasic *)($arg0)
+  else
+  if $types == 0x04
+    # RUBY_T_FLOAT
+    p "T_FLOAT:"
+    p coerce_ptr_to_double($arg0)
+  else
+  if $types == 0x05
+  # RUBY_T_STRING
+    p "T_STRING:"
+    p *(struct RString *)($arg0)
+  else
+  if $types == 0x06
+    # RUBY_T_REGEXP
+    p "T_REGEXP:"
+    p *(struct rb_regexp *)($arg0)
+  else
+  if $types == 0x07
+    # RUBY_T_ARRAY
+    p "T_ARRAY:"
+    p *(struct RArray *)($arg0)
+  else
+  if $types == 0x08
+    # RUBY_T_HASH
+    p "T_HASH:"
+    p *(struct RHash *)($arg0)
+  else
+  if $types == 0x09
+    # RUBY_T_STRUCT
+    p "T_STRUCT:"
+    p *(struct RStruct *)($arg0)
+  else
+  if $types == 0x0a
+    # RUBY_T_BIGNUM
+    p "T_BIGNUM:"
+    p *(struct RBignum *)($arg0)
+  else
+  if $types == 0x0b
+    # RUBY_T_FILE
+    p "T_FILE:"
+    p *(struct RFile *)($arg0)
+    p *((struct RFile *)($arg0))->fptr
+  else
+  if $types == 0x0c
+    # RUBY_T_DATA
+    p "T_DATA:"
+    p *(struct RData *)($arg0)
+  else
+  if $types == 0x0d
+    # RUBY_T_MATCH
+    p "T_MATCH:"
+    p *(struct rb_match *)($arg0)
+  else
+  if $types == 0x0e
+    # RUBY_T_COMPLEX
+    p "T_COMPLEX:"
+    p *(struct RComplex *)($arg0)
+  else
+  if $types == 0x0f
+    # RUBY_T_RATIONAL
+    p "T_RATIONAL:"
+    p *(struct RRational *)($arg0)
+  else
+  if $types == 0x11
+    # RUBY_T_NIL
+    p "T_NIL:"
+    p "nil"
+  else
+  if $types == 0x12
+    # RUBY_T_TRUE
+    p "T_TRUE:"
+    p "true"
+  else
+  if $types == 0x14
+    # RUBY_T_SYMBOL
+    p "T_SYMBOL:"
+    p *(struct rb_sym_t *)($arg0)
+  else
+  if $types == 0x15
+    # RUBY_T_FIXNUM
+    p "T_FIXNUM:"
+    p rb_num2int($arg0)
+  end
+  if $types == 0x1b
+    # RUBY_T_UNDEF
+    p "T_UNDEF:"
+    p "undef"
+  end
+
+end

HACKING.rdoc

@@ -173,3 +173,12 @@ The following environment variables might help you debug easy bugs.
 
 * To print the GC references of a given memory object:
   (gdb) info gc-references <address>
+
+* To print the content of Ruby object:
+  (gdb) rp <variable name of Ruby object>
+
+  ex)
+  (gdb) rp str
+  $1 = "T_STRING:"
+  $2 = {basic = {klass = 17183054944, flags = 0}, encoding = 0x40040a280, capacity_in_bytes = 6, length_in_bytes = 5, cached_length = 0, 
+    bytes = 0x40049e640 "hello", flags = 0 '\0'}