1 | <?xml version="1.0" standalone="yes"?> |
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2 | <!DOCTYPE library PUBLIC "-//Boost//DTD BoostBook XML V1.0//EN" |
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3 | "http://www.boost.org/tools/boostbook/dtd/boostbook.dtd" |
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4 | [ |
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5 | <!ENTITY % entities SYSTEM "program_options.ent" > |
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6 | %entities; |
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7 | ]> |
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8 | <section id="program_options.changes"> |
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9 | <title>Changes since formal review</title> |
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10 | |
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11 | <para>During formal review, a large number of changes was suggested. To make |
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12 | using the new version easier, the implemented changes are described |
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13 | below.</para> |
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14 | |
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15 | <para>Let's start with an example. The following is a typical code for the |
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16 | reviewed version:<programlisting> |
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17 | options_description desc; |
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18 | desc.add_options() |
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19 | ("magic", parameter<int>("value"), "magic value for the program") |
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20 | .default_value("43") |
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21 | |
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22 | variables_map vm; |
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23 | options_and_arguments oa1 = parse_command_line(ac, av, desc); |
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24 | store(oa1, vm, desc) |
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25 | |
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26 | variables_map vm2; |
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27 | ifstream ifs("main.cfg"); |
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28 | options_and_arguments oa2 = parse_config_file(ifs, desc); |
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29 | store(oa1, vm2, desc); |
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30 | |
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31 | vm.next(&vm2); |
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32 | </programlisting>The code for the current version would look like: |
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33 | <programlisting> |
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34 | options_description desc; |
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35 | desc.add_options() |
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36 | ("magic", value<int>()->default_value(43), |
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37 | "magic value for the program") |
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38 | |
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39 | variables_map vm; |
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40 | |
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41 | store(parse_command_line(ac, av, desc), vm); |
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42 | |
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43 | ifstream ifs("main.cfg"); |
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44 | store(parse_command_line(ifs, desc), vm); |
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45 | |
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46 | notify(vm); |
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47 | </programlisting> |
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48 | </para> |
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49 | |
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50 | <para>Let's examine all the changes in detail</para> |
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51 | |
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52 | <section> |
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53 | <title>Option description</title> |
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54 | |
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55 | <itemizedlist> |
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56 | <listitem> |
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57 | <para>The <code>parameter</code> function was renamed to |
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58 | <code>value</code>. Rationale: "paramater" is yet another term with no |
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59 | clear definition, while "value" is already used everywhere in |
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60 | docs.</para> |
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61 | </listitem> |
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62 | <listitem> |
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63 | <para>The default value is specified in different place, and should |
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64 | use the value of desired type, not string. Previous code was: |
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65 | <programlisting> |
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66 | ("magic", parameter<int>("value")).default_value("43") |
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67 | </programlisting> |
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68 | and the new code is |
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69 | <programlisting> |
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70 | ("magic", parameter<int>("value")->default_value(43)); |
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71 | </programlisting> |
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72 | Rationale: the new way is less restrictive. At the same time, the |
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73 | new design allows to implement other behaviour, like validation of |
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74 | the value, which require knowledge of the value type. |
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75 | </para> |
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76 | </listitem> |
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77 | |
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78 | <listitem> |
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79 | <para>The number of token value can take on command line, which was |
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80 | specified using character suffix appended to value name, is now |
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81 | specified using more explicit member calls. Moreover, it's not longer |
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82 | possible to specify the "value name". |
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83 | For example: |
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84 | <programlisting>("numbers", parameter<int>("n+"))</programlisting> |
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85 | has became |
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86 | <programlisting>("numbers", value<int>()->multitoken())</programlisting> |
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87 | Rationale: such modifiers tend to make command line usage less |
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88 | clear. There's no need to make evil things too easy to do. |
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89 | The "value name" had only two roles: specifying modifiers, and |
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90 | telling what to output in automated help. The first role has became |
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91 | obsolete, and the second was questionable too. It was very unclear how |
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92 | to decide on the best "value name", and eventually the selection was randon. |
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93 | </para> |
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94 | </listitem> |
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95 | </itemizedlist> |
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96 | |
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97 | </section> |
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98 | |
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99 | <section> |
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100 | <title>Parsers</title> |
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101 | |
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102 | |
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103 | <itemizedlist> |
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104 | <listitem> |
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105 | <para>The <code>options_and_argument</code> class was removed.</para> |
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106 | </listitem> |
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107 | <listitem> |
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108 | <para>The <code>cmdline</code> and <code>config_file</code> classes |
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109 | were removed from the public interface. Various command line styles |
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110 | are now declared in the <code>command_line_style</code> subnamespace. |
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111 | </para> |
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112 | </listitem> |
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113 | |
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114 | <listitem> |
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115 | <para>New function <code>parse_environment</code> was added.</para> |
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116 | </listitem> |
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117 | |
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118 | <listitem> |
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119 | <para>Support for positional options was added</para> |
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120 | </listitem> |
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121 | |
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122 | </itemizedlist> |
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123 | </section> |
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124 | |
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125 | |
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126 | <section> |
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127 | <title>Storage</title> |
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128 | |
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129 | <itemizedlist> |
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130 | <listitem> |
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131 | <para>The <code>notify</code> function should be called after all |
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132 | sources are stored in a <code>variales_map</code> instance. This is |
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133 | done to property support priority of configuration sources. |
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134 | </para> |
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135 | </listitem> |
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136 | </itemizedlist> |
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137 | </section> |
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138 | |
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139 | |
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140 | |
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141 | </section> |
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142 | |
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143 | <!-- |
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144 | Local Variables: |
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145 | mode: xml |
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146 | sgml-indent-data: t |
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147 | sgml-parent-document: ("program_options.xml" "section") |
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148 | sgml-set-face: t |
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149 | End: |
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150 | --> |
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