1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
|
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<HTML>
<HEAD>
<TITLE>AARM95 - Formal Types</TITLE>
<META NAME="Author" CONTENT="JTC1/SC22/WG9/ARG, by Randall Brukardt, ARG Editor">
<META NAME="GENERATOR" CONTENT="Arm_Form.Exe, Ada Reference Manual generator">
<STYLE type="text/css">
DIV.paranum {position: absolute; font-family: Arial, Helvetica, sans-serif; left: 0.5 em; top: auto}
TT {font-family: "Courier New", monospace}
DT {display: compact}
DIV.Normal {font-family: "Times New Roman", Times, serif; margin-bottom: 0.6em}
DIV.Wide {font-family: "Times New Roman", Times, serif; margin-top: 0.6em; margin-bottom: 0.6em}
DIV.Annotations {font-family: "Times New Roman", Times, serif; margin-left: 4.0em; margin-bottom: 0.6em}
DIV.WideAnnotations {font-family: "Times New Roman", Times, serif; margin-left: 4.0em; margin-top: 0.6em; margin-bottom: 0.6em}
DIV.Index {font-family: "Times New Roman", Times, serif}
DIV.SyntaxSummary {font-family: "Times New Roman", Times, serif; margin-left: 2.0em; margin-bottom: 0.4em}
DIV.Notes {font-family: "Times New Roman", Times, serif; margin-left: 2.0em; margin-bottom: 0.6em}
DIV.NotesHeader {font-family: "Times New Roman", Times, serif; margin-left: 2.0em}
DIV.SyntaxIndented {font-family: "Times New Roman", Times, serif; margin-left: 2.0em; margin-bottom: 0.4em}
DIV.Indented {font-family: "Times New Roman", Times, serif; margin-left: 6.0em; margin-bottom: 0.6em}
DIV.CodeIndented {font-family: "Times New Roman", Times, serif; margin-left: 4.0em; margin-bottom: 0.6em}
DIV.SmallIndented {font-family: "Times New Roman", Times, serif; margin-left: 10.0em; margin-bottom: 0.6em}
DIV.SmallCodeIndented {font-family: "Times New Roman", Times, serif; margin-left: 8.0em; margin-bottom: 0.6em}
DIV.Examples {font-family: "Courier New", monospace; margin-left: 2.0em; margin-bottom: 0.6em}
DIV.SmallExamples {font-family: "Courier New", monospace; font-size: 80%; margin-left: 7.5em; margin-bottom: 0.6em}
DIV.IndentedExamples {font-family: "Courier New", monospace; margin-left: 8.0em; margin-bottom: 0.6em}
DIV.SmallIndentedExamples {font-family: "Courier New", monospace; font-size: 80%; margin-left: 15.0em; margin-bottom: 0.6em}
UL.Bulleted {font-family: "Times New Roman", Times, serif; margin-left: 2.0em; margin-right: 2.0em; margin-top: 0em; margin-bottom: 0.5em}
UL.SmallBulleted {font-family: "Times New Roman", Times, serif; margin-left: 6.0em; margin-right: 6.0em; margin-top: 0em; margin-bottom: 0.5em}
UL.NestedBulleted {font-family: "Times New Roman", Times, serif; margin-left: 4.0em; margin-right: 4.0em; margin-top: 0em; margin-bottom: 0.5em}
UL.SmallNestedBulleted {font-family: "Times New Roman", Times, serif; margin-left: 8.0em; margin-right: 8.0em; margin-top: 0em; margin-bottom: 0.5em}
UL.IndentedBulleted {font-family: "Times New Roman", Times, serif; margin-left: 8.0em; margin-right: 8.0em; margin-top: 0em; margin-bottom: 0.5em}
UL.CodeIndentedBulleted {font-family: "Times New Roman", Times, serif; margin-left: 6.0em; margin-right: 6.0em; margin-top: 0em; margin-bottom: 0.5em}
UL.CodeIndentedNestedBulleted {font-family: "Times New Roman", Times, serif; margin-left: 8.0em; margin-right: 8.0em; margin-top: 0em; margin-bottom: 0.5em}
UL.SyntaxIndentedBulleted {font-family: "Times New Roman", Times, serif; margin-left: 4.0em; margin-right: 4.0em; margin-top: 0em; margin-bottom: 0.5em}
UL.NotesBulleted {font-family: "Times New Roman", Times, serif; margin-left: 4.0em; margin-right: 4.0em; margin-top: 0em; margin-bottom: 0.5em}
UL.NotesNestedBulleted {font-family: "Times New Roman", Times, serif; margin-left: 6.0em; margin-right: 6.0em; margin-top: 0em; margin-bottom: 0.5em}
DL.Hanging {font-family: "Times New Roman", Times, serif; margin-top: 0em; margin-bottom: 0.6em}
DD.Hanging {margin-left: 6.0em}
DL.IndentedHanging {font-family: "Times New Roman", Times, serif; margin-left: 4.0em; margin-top: 0em; margin-bottom: 0.6em}
DD.IndentedHanging {margin-left: 2.0em}
DL.HangingInBulleted {font-family: "Times New Roman", Times, serif; margin-left: 2.0em; margin-right: 2.0em; margin-top: 0em; margin-bottom: 0.5em}
DD.HangingInBulleted {margin-left: 4.0em}
DL.SmallHanging {font-family: "Times New Roman", Times, serif; margin-left: 4.0em; margin-top: 0em; margin-bottom: 0.6em}
DD.SmallHanging {margin-left: 7.5em}
DL.SmallIndentedHanging {font-family: "Times New Roman", Times, serif; margin-left: 8.0em; margin-top: 0em; margin-bottom: 0.6em}
DD.SmallIndentedHanging {margin-left: 2.0em}
DL.SmallHangingInBulleted {font-family: "Times New Roman", Times, serif; margin-left: 6.0em; margin-right: 6.0em; margin-top: 0em; margin-bottom: 0.5em}
DD.SmallHangingInBulleted {margin-left: 5.0em}
DL.Enumerated {font-family: "Times New Roman", Times, serif; margin-right: 0.0em; margin-top: 0em; margin-bottom: 0.5em}
DD.Enumerated {margin-left: 2.0em}
DL.SmallEnumerated {font-family: "Times New Roman", Times, serif; margin-left: 4.0em; margin-right: 4.0em; margin-top: 0em; margin-bottom: 0.5em}
DD.SmallEnumerated {margin-left: 2.5em}
DL.NestedEnumerated {font-family: "Times New Roman", Times, serif; margin-left: 2.0em; margin-right: 2.0em; margin-top: 0em; margin-bottom: 0.5em}
DL.SmallNestedEnumerated {font-family: "Times New Roman", Times, serif; margin-left: 6.0em; margin-right: 6.0em; margin-top: 0em; margin-bottom: 0.5em}
</STYLE>
</HEAD>
<BODY TEXT="#000000" BGCOLOR="#FFFFF0" LINK="#0000FF" VLINK="#800080" ALINK="#FF0000">
<P><A HREF="AA-TOC.html">Contents</A> <A HREF="AA-0-29.html">Index</A> <A HREF="AA-12-4.html">Previous</A> <A HREF="AA-12-5-1.html">Next</A></P>
<HR>
<H1> 12.5 Formal Types</H1>
<DIV Class="Paranum"><FONT SIZE=-2>1</FONT></DIV>
<DIV Class="Normal"> [A generic formal subtype can be used to pass
to a generic unit a subtype whose type is in a certain class of types.]
</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>1.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Reason: </B>We considered having
intermediate syntactic categories <FONT FACE="Arial, Helvetica">formal_integer_type_definition</FONT>,
<FONT FACE="Arial, Helvetica">formal_real_type_definition</FONT>, and
<FONT FACE="Arial, Helvetica">formal_fixed_point_definition</FONT>, to
be more uniform with the syntax rules for non-generic-formal types. However,
that would make the rules for formal types slightly more complicated,
and it would cause confusion, since <FONT FACE="Arial, Helvetica">formal_discrete_type_definition</FONT>
would not fit into the scheme very well. </FONT></DIV>
<H4 ALIGN=CENTER>Syntax</H4>
<DIV Class="Paranum"><FONT SIZE=-2>2</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">formal_type_declaration<A NAME="I4253"></A>
::= </FONT><BR>
<B>type</B> <A NAME="I4254"></A><FONT FACE="Arial, Helvetica">defining_identifier</FONT>[<A NAME="I4255"></A><FONT FACE="Arial, Helvetica">discriminant_part</FONT>] <B>is</B> <A NAME="I4256"></A><FONT FACE="Arial, Helvetica">formal_type_definition</FONT>;</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>3</FONT></DIV>
<DIV Class="SyntaxIndented"><FONT FACE="Arial, Helvetica">formal_type_definition<A NAME="I4257"></A>
::= </FONT><BR>
<A NAME="I4258"></A><FONT FACE="Arial, Helvetica">formal_private_type_definition</FONT><BR>
| <A NAME="I4259"></A><FONT FACE="Arial, Helvetica">formal_derived_type_definition</FONT><BR>
| <A NAME="I4260"></A><FONT FACE="Arial, Helvetica">formal_discrete_type_definition</FONT><BR>
| <A NAME="I4261"></A><FONT FACE="Arial, Helvetica">formal_signed_integer_type_definition</FONT><BR>
| <A NAME="I4262"></A><FONT FACE="Arial, Helvetica">formal_modular_type_definition</FONT><BR>
| <A NAME="I4263"></A><FONT FACE="Arial, Helvetica">formal_floating_point_definition</FONT><BR>
| <A NAME="I4264"></A><FONT FACE="Arial, Helvetica">formal_ordinary_fixed_point_definition</FONT><BR>
| <A NAME="I4265"></A><FONT FACE="Arial, Helvetica">formal_decimal_fixed_point_definition</FONT><BR>
| <A NAME="I4266"></A><FONT FACE="Arial, Helvetica">formal_array_type_definition</FONT><BR>
| <A NAME="I4267"></A><FONT FACE="Arial, Helvetica">formal_access_type_definition</FONT></DIV>
<H4 ALIGN=CENTER>Legality Rules</H4>
<DIV Class="Paranum"><FONT SIZE=-2>4</FONT></DIV>
<DIV Class="Normal"> <A NAME="I4268"></A><A NAME="I4269"></A><A NAME="I4270"></A><A NAME="I4271"></A>For
a generic formal subtype, the actual shall be a <FONT FACE="Arial, Helvetica">subtype_mark</FONT>;
it denotes the <I>(generic) actual subtype</I>. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>When we say
simply ``formal'' or ``actual'' (for a generic formal that denotes a
subtype) we're talking about the subtype, not the type, since a name
that denotes a <FONT FACE="Arial, Helvetica">formal_type_declaration</FONT>
denotes a subtype, and the corresponding actual also denotes a subtype.
</FONT></DIV>
<H4 ALIGN=CENTER>Static Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>5</FONT></DIV>
<DIV Class="Normal"> <A NAME="I4272"></A><A NAME="I4273"></A><A NAME="I4274"></A><A NAME="I4275"></A>A
<FONT FACE="Arial, Helvetica">formal_type_declaration</FONT> declares
a <I>(generic) formal type</I>, and its first subtype, the <I>(generic)
formal subtype</I>. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>5.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>A subtype
(other than the first subtype) of a generic formal type is not a generic
formal subtype. </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>6</FONT></DIV>
<DIV Class="Normal"> <A NAME="I4276"></A><A NAME="I4277"></A>The form
of a <FONT FACE="Arial, Helvetica">formal_type_definition</FONT> <I>determines
a class</I> to which the formal type belongs. For a <FONT FACE="Arial, Helvetica">formal_private_type_definition</FONT>
the reserved words <B>tagged</B> and <B>limited</B> indicate the class
(see <A HREF="AA-12-5-1.html">12.5.1</A>). For a <FONT FACE="Arial, Helvetica">formal_derived_type_definition</FONT>
the class is the derivation class rooted at the ancestor type. For other
formal types, the name of the syntactic category indicates the class;
a <FONT FACE="Arial, Helvetica">formal_discrete_type_definition</FONT>
defines a discrete type, and so on. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>6.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Reason: </B>This rule is clearer
with the flat syntax rule for <FONT FACE="Arial, Helvetica">formal_type_definition</FONT>
given above. Adding <FONT FACE="Arial, Helvetica">formal_integer_type_definition</FONT>
and others would make this rule harder to state clearly. </FONT></DIV>
<H4 ALIGN=CENTER>Legality Rules</H4>
<DIV Class="Paranum"><FONT SIZE=-2>7</FONT></DIV>
<DIV Class="Normal"> The actual type shall be in the class determined
for the formal. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>7.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>For example,
if the class determined for the formal is the class of all discrete types,
then the actual has to be discrete.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>7.b</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>Note that this rule does not require
the actual to belong to every class to which the formal belongs. For
example, formal private types are in the class of composite types, but
the actual need not be composite. Furthermore, one can imagine an infinite
number of classes that are just arbitrary sets of types that obey the
closed-under-derivation rule, and are therefore technically classes (even
though we don't give them names, since they are uninteresting). We don't
want this rule to apply to <I>those</I> classes.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>7.c</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>``Limited'' is not a ``interesting''
class, but ``nonlimited'' is; it is legal to pass a nonlimited type to
a limited formal type, but not the other way around. The reserved word
<FONT FACE="Arial, Helvetica">limited</FONT> really represents a class
containing both limited and nonlimited types. ``Private'' is not a class;
a generic formal private type accepts both private and nonprivate actual
types.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>7.d</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>It is legal to pass a class-wide
subtype as the actual if it is in the right class, so long as the formal
has unknown discriminants. </FONT></DIV>
<H4 ALIGN=CENTER>Static Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>8/1</FONT></DIV>
<DIV Class="Normal"> {<I><A HREF="defect1.html#8652/0037">8652/0037</A></I>}
[The formal type also belongs to each class that contains the determined
class.] The primitive subprograms of the type are as for any type in
the determined class. For a formal type other than a formal derived type,
these are the predefined operators of the type<U>. For an elementary
formal type, the predefined operators are implicitly declared immediately
after the declaration of the formal type. For a composite formal type,
the predefined operators are implicitly declared either immediately after
the declaration of the formal type, or later in its immediate scope according
to the rules of <A HREF="AA-7-3-1.html">7.3.1</A>.</U><S>; they are implicitly
declared immediately after the declaration of the formal type.</S> In
an instance, the copy of such an implicit declaration declares a view
of the predefined operator of the actual type, even if this operator
has been overridden for the actual type. [The rules specific to formal
derived types are given in <A HREF="AA-12-5-1.html">12.5.1</A>.] </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>8.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>All properties
of the type are as for any type in the class. Some examples: The primitive
operations available are as defined by the language for each class. The
form of <FONT FACE="Arial, Helvetica">constraint</FONT> applicable to
a formal type in a <FONT FACE="Arial, Helvetica">subtype_indication</FONT>
depends on the class of the type as for a nonformal type. The formal
type is tagged if and only if it is declared as a tagged private type,
or as a type derived from a (visibly) tagged type. (Note that the actual
type might be tagged even if the formal type is not.) </FONT></DIV>
<DIV Class="NotesHeader"><FONT SIZE=-1>NOTES</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>9</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>7 Generic formal types, like
all types, are not named. Instead, a <FONT FACE="Arial, Helvetica">name</FONT>
can denote a generic formal subtype. Within a generic unit, a generic
formal type is considered as being distinct from all other (formal or
nonformal) types. </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>9.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Proof: </B>This follows from
the fact that each <FONT FACE="Arial, Helvetica">formal_type_declaration</FONT>
declares a type. </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>10</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>8 A <FONT FACE="Arial, Helvetica">discriminant_part</FONT>
is allowed only for certain kinds of types, and therefore only for certain
kinds of generic formal types. See <A HREF="AA-3-7.html">3.7</A>. </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>10.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>The term
``formal floating point type'' refers to a type defined by a <FONT FACE="Arial, Helvetica">formal_floating_point_definition</FONT>.
It does not include a formal derived type whose ancestor is floating
point. Similar terminology applies to the other kinds of <FONT FACE="Arial, Helvetica">formal_type_definition</FONT>.
</FONT></DIV>
<H4 ALIGN=CENTER>Examples</H4>
<DIV Class="Paranum"><FONT SIZE=-2>11</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> <I>Examples of
generic formal types:</I> </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>12</FONT></DIV>
<DIV Class="Examples"><TT><B>type</B> Item <B>is</B> <B>private</B>;<BR>
<B>type</B> Buffer(Length : Natural) <B>is</B> <B>limited</B> <B>private</B>;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>13</FONT></DIV>
<DIV Class="Examples"><TT><B>type</B> Enum <B>is</B> (<>);<BR>
<B>type</B> Int <B>is</B> <B>range</B> <>;<BR>
<B>type</B> Angle <B>is</B> <B>delta</B> <>;<BR>
<B>type</B> Mass <B>is</B> <B>digits</B> <>;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>14</FONT></DIV>
<DIV Class="Examples"><TT><B>type</B> Table <B>is</B> <B>array</B> (Enum) <B>of</B> Item;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>15</FONT></DIV>
<DIV Class="Wide" Style="margin-bottom: 0.4em"> <I>Example of a generic
formal part declaring a formal integer type:</I> </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>16</FONT></DIV>
<DIV Class="Examples"><TT><B>generic</B><BR>
<B>type</B> Rank <B>is</B> <B>range</B> <>;<BR>
First : Rank := Rank'First;<BR>
Second : Rank := First + 1; --<I> the operator "+" of the type Rank </I></TT></DIV>
<H4 ALIGN=CENTER>Wording Changes from Ada 83</H4>
<DIV Class="Paranum"><FONT SIZE=-2>16.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>RM83 has separate sections ``Generic
Formal Xs'' and ``Matching Rules for Formal Xs'' (for various X's) with
most of the text redundant between the two. We have combined the two
in order to reduce the redundancy. In RM83, there is no ``Matching Rules
for Formal Types'' section; nor is there a ``Generic Formal Y Types''
section (for Y = Private, Scalar, Array, and Access). This causes, for
example, the duplication across all the ``Matching Rules for Y Types''
sections of the rule that the actual passed to a formal type shall be
a subtype; the new organization avoids that problem.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>16.b</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>The matching rules are stated
more concisely.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>16.c</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>We no longer consider the multiplying
operators that deliver a result of type <I>universal_fixed</I> to be
predefined for the various types; there is only one of each in package
Standard. Therefore, we need not mention them here as RM83 had to. </FONT></DIV>
<HR>
<P><A HREF="AA-TOC.html">Contents</A> <A HREF="AA-0-29.html">Index</A> <A HREF="AA-12-4.html">Previous</A> <A HREF="AA-12-5-1.html">Next</A> <A HREF="AA-TTL.html">Legal</A></P>
</BODY>
</HTML>
|
