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
|
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN""http://www.w3.org/TR/html4/loose.dtd">
<HTML
><HEAD
><TITLE
>How do I express conflicts?</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK
REL="HOME"
TITLE="The findlib User's Guide"
HREF="index.html"><LINK
REL="UP"
TITLE="FAQs"
HREF="c429.html"><LINK
REL="PREVIOUS"
TITLE="Why do some people install the .cmx files?"
HREF="x524.html"></HEAD
><BODY
CLASS="SECT1"
BGCOLOR="#FFFFFF"
TEXT="#000000"
LINK="#0000FF"
VLINK="#840084"
ALINK="#0000FF"
><DIV
CLASS="NAVHEADER"
><TABLE
SUMMARY="Header navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="3"
ALIGN="center"
>The findlib User's Guide</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="bottom"
><A
HREF="x524.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="80%"
ALIGN="center"
VALIGN="bottom"
>Chapter 7. FAQs</TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="bottom"
> </TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="AEN528"
>How do I express conflicts?</A
></H1
><P
>A conflict means that a certain combination of packages
and package features will not work. A number of conflict conditions
can be expressed:</P
><P
></P
><UL
><LI
><P
>To state that a package will not work if a certain
predicate is set, use the <TT
CLASS="LITERAL"
>error</TT
> variable. For example,
when package p does not work for multi-threaded programs:
<PRE
CLASS="PROGRAMLISTING"
>error(mt) = "Package p is incompatible with multi-threaded programs"</PRE
>
This works for other standard predicates, too.</P
></LI
><LI
><P
>To state that a package will not work together with
another package, it is possible to make <TT
CLASS="LITERAL"
>error</TT
> dependent
on package predicates. For example, when package p does not work
together with q:
<PRE
CLASS="PROGRAMLISTING"
>error(pkg_q) = "Package p is incompatible with package q"</PRE
>
This also works with subpackages (e.g. <TT
CLASS="LITERAL"
>pkg_q.q_sub</TT
>).
</P
></LI
><LI
><P
>If an error is too much, it might be a good idea to
just inform the user about possible problems. In this case
you can emit a warning instead:
</P
><PRE
CLASS="PROGRAMLISTING"
>warning(pkg_q) = "Using package p and q together is a really bad idea"</PRE
></LI
></UL
><P
>Note that such error conditions should only be added if there is
absolutely no chance to get the combination of packages and features running.
For example, in the case of multi-threaded programs it is often possible
to add wrappers around unsafe libraries to fix the incompatibility.
</P
><P
>It is not possible to express incompatibilities between package
versions. Such incompatibilities should be detected when software is
installed, not when it is used.</P
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
SUMMARY="Footer navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="x524.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="index.html"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
> </TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Why do some people install the .cmx files?</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="c429.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
> </TD
></TR
></TABLE
></DIV
></BODY
></HTML
>
|
