From Jason Turner

[dcl.fct.def.delete]

C++17 → C++20 3.9 KB 45 lines
Current Draft | LaTeX Source
Archived: C++17 | C++20
Markdown: C++17 | C++20
Explore in Adventure Game
C++ Weekly: Ep 107 | Ep 471 | Ep 126

Diff to HTML by rtfpessoa

Files changed (1) hide show
  1. tmp/tmpruz2_3d4/{from.md → to.md} +18 -22
tmp/tmpruz2_3d4/{from.md → to.md} RENAMED
@@ -1,36 +1,32 @@
1
  ### Deleted definitions <a id="dcl.fct.def.delete">[[dcl.fct.def.delete]]</a>
2
 
3
- A function definition of the form:
4
-
5
- ``` bnf
6
- attribute-specifier-seqₒₚₜ decl-specifier-seqₒₚₜ declarator virt-specifier-seqₒₚₜ ' = delete ;'
7
- ```
8
-
9
  is called a *deleted definition*. A function with a deleted definition
10
  is also called a *deleted function*.
11
 
12
  A program that refers to a deleted function implicitly or explicitly,
13
  other than to declare it, is ill-formed.
14
 
15
  [*Note 1*: This includes calling the function implicitly or explicitly
16
  and forming a pointer or pointer-to-member to the function. It applies
17
  even for references in expressions that are not potentially-evaluated.
18
  If a function is overloaded, it is referenced only if the function is
19
- selected by overload resolution. The implicit odr-use (
20
- [[basic.def.odr]]) of a virtual function does not, by itself, constitute
21
- a reference. — *end note*]
22
 
23
  [*Example 1*:
24
 
25
- One can enforce non-default-initialization and non-integral
26
- initialization with
27
 
28
  ``` cpp
29
  struct onlydouble {
30
  onlydouble() = delete; // OK, but redundant
31
- onlydouble(std::intmax_t) = delete;
 
32
  onlydouble(double);
33
  };
34
  ```
35
 
36
  — *end example*]
@@ -43,19 +39,19 @@ deleted definitions of a user-declared `operator new` for that class.
43
  ``` cpp
44
  struct sometype {
45
  void* operator new(std::size_t) = delete;
46
  void* operator new[](std::size_t) = delete;
47
  };
48
- sometype* p = new sometype; // error, deleted class operator new
49
- sometype* q = new sometype[3]; // error, deleted class operator new[]
50
  ```
51
 
52
  — *end example*]
53
 
54
  [*Example 3*:
55
 
56
- One can make a class uncopyable, i.e. move-only, by using deleted
57
  definitions of the copy constructor and copy assignment operator, and
58
  then providing defaulted definitions of the move constructor and move
59
  assignment operator.
60
 
61
  ``` cpp
@@ -66,32 +62,32 @@ struct moveonly {
66
  moveonly& operator=(const moveonly&) = delete;
67
  moveonly& operator=(moveonly&&) = default;
68
  ~moveonly() = default;
69
  };
70
  moveonly* p;
71
- moveonly q(*p); // error, deleted copy constructor
72
  ```
73
 
74
  — *end example*]
75
 
76
- A deleted function is implicitly an inline function ([[dcl.inline]]).
77
 
78
- [*Note 2*: The one-definition rule ([[basic.def.odr]]) applies to
79
- deleted definitions. — *end note*]
80
 
81
  A deleted definition of a function shall be the first declaration of the
82
  function or, for an explicit specialization of a function template, the
83
  first declaration of that specialization. An implicitly declared
84
- allocation or deallocation function ([[basic.stc.dynamic]]) shall not
85
- be defined as deleted.
86
 
87
  [*Example 4*:
88
 
89
  ``` cpp
90
  struct sometype {
91
  sometype();
92
  };
93
- sometype::sometype() = delete; // ill-formed; not first declaration
94
  ```
95
 
96
  — *end example*]
97
 
 
1
  ### Deleted definitions <a id="dcl.fct.def.delete">[[dcl.fct.def.delete]]</a>
2
 
3
+ A function definition whose *function-body* is of the form `= delete ;`
 
 
 
 
 
4
  is called a *deleted definition*. A function with a deleted definition
5
  is also called a *deleted function*.
6
 
7
  A program that refers to a deleted function implicitly or explicitly,
8
  other than to declare it, is ill-formed.
9
 
10
  [*Note 1*: This includes calling the function implicitly or explicitly
11
  and forming a pointer or pointer-to-member to the function. It applies
12
  even for references in expressions that are not potentially-evaluated.
13
  If a function is overloaded, it is referenced only if the function is
14
+ selected by overload resolution. The implicit odr-use [[basic.def.odr]]
15
+ of a virtual function does not, by itself, constitute a
16
+ reference. — *end note*]
17
 
18
  [*Example 1*:
19
 
20
+ One can prevent default initialization and initialization by
21
+ non-`double`s with
22
 
23
  ``` cpp
24
  struct onlydouble {
25
  onlydouble() = delete; // OK, but redundant
26
+ template<class T>
27
+ onlydouble(T) = delete;
28
  onlydouble(double);
29
  };
30
  ```
31
 
32
  — *end example*]
 
39
  ``` cpp
40
  struct sometype {
41
  void* operator new(std::size_t) = delete;
42
  void* operator new[](std::size_t) = delete;
43
  };
44
+ sometype* p = new sometype; // error: deleted class operator new
45
+ sometype* q = new sometype[3]; // error: deleted class operator new[]
46
  ```
47
 
48
  — *end example*]
49
 
50
  [*Example 3*:
51
 
52
+ One can make a class uncopyable, i.e., move-only, by using deleted
53
  definitions of the copy constructor and copy assignment operator, and
54
  then providing defaulted definitions of the move constructor and move
55
  assignment operator.
56
 
57
  ``` cpp
 
62
  moveonly& operator=(const moveonly&) = delete;
63
  moveonly& operator=(moveonly&&) = default;
64
  ~moveonly() = default;
65
  };
66
  moveonly* p;
67
+ moveonly q(*p); // error: deleted copy constructor
68
  ```
69
 
70
  — *end example*]
71
 
72
+ A deleted function is implicitly an inline function [[dcl.inline]].
73
 
74
+ [*Note 2*: The one-definition rule [[basic.def.odr]] applies to deleted
75
+ definitions. — *end note*]
76
 
77
  A deleted definition of a function shall be the first declaration of the
78
  function or, for an explicit specialization of a function template, the
79
  first declaration of that specialization. An implicitly declared
80
+ allocation or deallocation function [[basic.stc.dynamic]] shall not be
81
+ defined as deleted.
82
 
83
  [*Example 4*:
84
 
85
  ``` cpp
86
  struct sometype {
87
  sometype();
88
  };
89
+ sometype::sometype() = delete; // error: not first declaration
90
  ```
91
 
92
  — *end example*]
93