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 *
__go_convert_interface_2(const struct __go_type_descriptor * lhs_descriptor,const struct __go_type_descriptor * rhs_descriptor,_Bool may_fail)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 *
__go_convert_interface(const struct __go_type_descriptor * lhs_descriptor,const struct __go_type_descriptor * rhs_descriptor)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 }
133