blob: c7ed8fc4badb9851011257cf939d614f2ddd1c3f (
plain)
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
|
<!--
Licensed to the Apache Software Foundation (ASF) under one or more
contributor license agreements. See the NOTICE file distributed with
this work for additional information regarding copyright ownership.
The ASF licenses this file to You under the Apache License, Version 2.0
(the "License"); you may not use this file except in compliance with
the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
-->
<html>
<head>
<meta http-equiv="Content-Language" content="en-us">
<link rel="stylesheet" type="text/css" href="../stylesheets/style.css">
<title>Local Task</title>
</head>
<body>
<h2>Local</h2>
<h3>Description</h3>
<p>Adds a local property to the current scope. Property scopes exist at Apache Ant's
various "block" levels. These include targets as well as the
<a href="parallel.html">Parallel</a> and <a href="sequential.html">Sequential</a>
task containers (including <a href="macrodef.html">Macrodef</a> bodies). A local
property at a given scope "shadows" properties of the same name at higher scopes,
including the global scope. Note that using the Local task at the global
level effectively makes the property local to the "anonymous target" in which
top-level operations are carried out; it will not be defined for other targets
in the buildfile. <b>Since Ant 1.8</b></p>
<p>A property is made local if the <code><local></code> task
precedes its definition. See the examples section.</p>
<h3>Parameters</h3>
<table border="1" cellpadding="2" cellspacing="0">
<tr>
<td valign="top"><b>Attribute</b></td>
<td valign="top"><b>Description</b></td>
<td align="center" valign="top"><b>Required</b></td>
</tr>
<tr>
<td valign="top">name</td>
<td valign="top">The property to declare in the current scope</td>
<td valign="top" align="center">Yes</td>
</tr>
</table>
<h3>Examples</h3>
<h4>Temporarily shadow a global property's value</h4>
<pre>
<property name="foo" value="foo"/>
<target name="step1">
<echo>Before local: foo is ${foo}</echo>
<local name="foo"/>
<property name="foo" value="bar"/>
<echo>After local: foo is ${foo}</echo>
</target>
<target name="step2" depends="step1">
<echo>In step2: foo is ${foo}</echo>
</target>
</pre>
<p>outputs</p>
<pre>
step1:
[echo] Before local: foo is foo
[echo] After local: foo is bar
step2:
[echo] In step2: foo is foo
</pre>
<p>here the local-task shadowed the global definition
of <code>foo</code> for the remainder of the target step1.</p>
<h4>Creating thread local properties</h4>
<pre>
<property name="foo" value="foo"/>
<parallel>
<echo>global 1: foo is ${foo}</echo>
<sequential>
<local name="foo"/>
<property name="foo" value="bar.1"/>
<echo>First sequential: foo is ${foo}</echo>
</sequential>
<sequential>
<sleep seconds="1"/>
<echo>global 2: foo is ${foo}</echo>
</sequential>
<sequential>
<local name="foo"/>
<property name="foo" value="bar.2"/>
<echo>Second sequential: foo is ${foo}</echo>
</sequential>
<echo>global 3: foo is ${foo}</echo>
</parallel>
</pre>
<p>outputs something similar to</p>
<pre>
[echo] global 3: foo is foo
[echo] global 1: foo is foo
[echo] First sequential: foo is bar.1
[echo] Second sequential: foo is bar.2
[echo] global 2: foo is foo
</pre>
<h4>Use inside macrodef</h4>
<p>This probably is where local can be applied in the most useful
way. If you needed a "temporary property" inside a macrodef in Ant
prior to Ant 1.8.0 you had to try to come up with a property name
that would be unique across macro invocations.</p>
<p>Say you wanted to write a macro that created the parent directory
of a given file. A naive approach would be:</p>
<pre>
<macrodef name="makeparentdir">
<attribute name="file"/>
<sequential>
<dirname property="parent" file="@{file}"/>
<mkdir dir="${parent}"/>
</sequential>
</macrodef>
<makeparentdir file="some-dir/some-file"/>
</pre>
<p>but this would create a global property "parent" on the first
invocation - and since properties are not mutable, any subsequent
invocation will see the same value and try to create the same
directory as the first invocation.</p>
<p>The recommendation prior to Ant 1.8.0 was to use a property name
based on one of the macro's attributes, like</p>
<pre>
<macrodef name="makeparentdir">
<attribute name="file"/>
<sequential>
<dirname property="parent.@{file}" file="@{file}"/>
<mkdir dir="${parent.@{file}}"/>
</sequential>
</macrodef>
</pre>
<p>Now invocations for different files will set different properties
and the directories will get created. Unfortunately this "pollutes"
the global properties space. In addition it may be hard to come up
with unique names in some cases.</p>
<p>Enter <code><local></code>:</p>
<pre>
<macrodef name="makeparentdir">
<attribute name="file"/>
<sequential>
<local name="parent"/>
<dirname property="parent" file="@{file}"/>
<mkdir dir="${parent}"/>
</sequential>
</macrodef>
</pre>
<p>Each invocation gets its own property name "parent" and there will
be no global property of that name at all.</p>
</body>
</html>
|
