libgo/runtime/go-convert-interface.c

   1 /* go-convert-interface.c -- convert interfaces for Go.
   2
   3    Copyright 2009 The Go Authors. All rights reserved.
   4    Use of this source code is governed by a BSD-style
   5    license that can be found in the LICENSE file.  */
   6
   7 #include "runtime.h"
   8 #include "go-alloc.h"
   9 #include "go-assert.h"
  10 #include "go-panic.h"
  11 #include "go-string.h"
  12 #include "go-type.h"
  13 #include "interface.h"
  14
  15 /* This is called when converting one interface type into another
  16    interface type.  LHS_DESCRIPTOR is the type descriptor of the
  17    resulting interface.  RHS_DESCRIPTOR is the type descriptor of the
  18    object being converted.  This builds and returns a new interface
  19    method table.  If any method in the LHS_DESCRIPTOR interface is not
  20    implemented by the object, the conversion fails.  If the conversion
  21    fails, then if MAY_FAIL is true this returns NULL; otherwise, it
  22    panics.  */
  23
  24 void *
  25 __go_convert_interface_2 (const struct __go_type_descriptor *lhs_descriptor,
  26                           const struct __go_type_descriptor *rhs_descriptor,
  27                           _Bool may_fail)
  28 {
  29   const struct __go_interface_type *lhs_interface;
  30   int lhs_method_count;
  31   const struct __go_interface_method* lhs_methods;
  32   const void **methods;
  33   const struct __go_uncommon_type *rhs_uncommon;
  34   int rhs_method_count;
  35   const struct __go_method *p_rhs_method;
  36   int i;
  37
  38   if (rhs_descriptor == NULL)
  39     {
  40       /* A nil value always converts to nil.  */
  41       return NULL;
  42     }
  43
  44   __go_assert ((lhs_descriptor->__code & GO_CODE_MASK) == GO_INTERFACE);
  45   lhs_interface = (const struct __go_interface_type *) lhs_descriptor;
  46   lhs_method_count = lhs_interface->__methods.__count;
  47   lhs_methods = ((const struct __go_interface_method *)
  48                  lhs_interface->__methods.__values);
  49
  50   /* This should not be called for an empty interface.  */
  51   __go_assert (lhs_method_count > 0);
  52
  53   rhs_uncommon = rhs_descriptor->__uncommon;
  54   if (rhs_uncommon == NULL || rhs_uncommon->__methods.__count == 0)
  55     {
  56       struct __go_empty_interface panic_arg;
  57
  58       if (may_fail)
  59         return NULL;
  60
  61       runtime_newTypeAssertionError (NULL, rhs_descriptor->__reflection,
  62                                      lhs_descriptor->__reflection,
  63                                      lhs_methods[0].__name,
  64                                      &panic_arg);
  65       __go_panic (panic_arg);
  66     }
  67
  68   rhs_method_count = rhs_uncommon->__methods.__count;
  69   p_rhs_method = ((const struct __go_method *)
  70                   rhs_uncommon->__methods.__values);
  71
  72   methods = NULL;
  73
  74   for (i = 0; i < lhs_method_count; ++i)
  75     {
  76       const struct __go_interface_method *p_lhs_method;
  77
  78       p_lhs_method = &lhs_methods[i];
  79
  80       while (rhs_method_count > 0
  81              && (!__go_ptr_strings_equal (p_lhs_method->__name,
  82                                           p_rhs_method->__name)
  83                  || !__go_ptr_strings_equal (p_lhs_method->__pkg_path,
  84                                              p_rhs_method->__pkg_path)))
  85         {
  86           ++p_rhs_method;
  87           --rhs_method_count;
  88         }
  89
  90       if (rhs_method_count == 0
  91           || !__go_type_descriptors_equal (p_lhs_method->__type,
  92                                            p_rhs_method->__mtype))
  93         {
  94           struct __go_empty_interface panic_arg;
  95
  96           if (methods != NULL)
  97             __go_free (methods);
  98
  99           if (may_fail)
 100             return NULL;
 101
 102           runtime_newTypeAssertionError (NULL, rhs_descriptor->__reflection,
 103                                          lhs_descriptor->__reflection,
 104                                          p_lhs_method->__name, &panic_arg);
 105           __go_panic (panic_arg);
 106         }
 107
 108       if (methods == NULL)
 109         {
 110           methods = (const void **) __go_alloc ((lhs_method_count + 1)
 111                                                 * sizeof (void *));
 112
 113           /* The first field in the method table is always the type of
 114              the object.  */
 115           methods[0] = rhs_descriptor;
 116         }
 117
 118       methods[i + 1] = p_rhs_method->__function;
 119     }
 120
 121   return methods;
 122 }
 123
 124 /* This is called by the compiler to convert a value from one
 125    interface type to another.  */
 126
 127 void *
 128 __go_convert_interface (const struct __go_type_descriptor *lhs_descriptor,
 129                         const struct __go_type_descriptor *rhs_descriptor)
 130 {
 131   return __go_convert_interface_2 (lhs_descriptor, rhs_descriptor, 0);
 132 }