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1 @c Copyright (C) 1996, 1997 John W. Eaton |
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2 @c This is part of the Octave manual. |
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3 @c For copying conditions, see the file gpl.texi. |
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4 |
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5 @node Tips |
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6 @appendix Tips and Standards |
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7 @cindex tips |
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8 @cindex standards of coding style |
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9 @cindex coding standards |
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10 |
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11 This chapter describes no additional features of Octave. Instead it |
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12 gives advice on making effective use of the features described in the |
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13 previous chapters. |
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14 |
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15 @menu |
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16 * Style Tips:: Writing clean and robust programs. |
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17 * Coding Tips:: Making code run faster. |
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18 * Documentation Tips:: Writing readable documentation strings. |
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19 * Comment Tips:: Conventions for writing comments. |
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20 * Function Headers:: Standard headers for functions. |
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21 @end menu |
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22 |
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23 @node Style Tips |
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24 @section Writing Clean Octave Programs |
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25 |
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26 Here are some tips for avoiding common errors in writing Octave code |
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27 intended for widespread use: |
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28 |
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29 @itemize @bullet |
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30 @item |
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31 Since all global variables share the same name space, and all functions |
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32 share another name space, you should choose a short word to distinguish |
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33 your program from other Octave programs. Then take care to begin the |
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34 names of all global variables, constants, and functions with the chosen |
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35 prefix. This helps avoid name conflicts. |
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36 |
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37 If you write a function that you think ought to be added to Octave under |
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38 a certain name, such as @code{fiddle_matrix}, don't call it by that name |
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39 in your program. Call it @code{mylib_fiddle_matrix} in your program, |
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40 and send mail to @email{maintainers@@octave.org} suggesting that it |
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41 be added to Octave. If and when it is, the name can be changed easily |
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42 enough. |
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43 |
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44 If one prefix is insufficient, your package may use two or three |
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45 alternative common prefixes, so long as they make sense. |
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46 |
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47 Separate the prefix from the rest of the symbol name with an underscore |
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48 @samp{_}. This will be consistent with Octave itself and with most |
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49 Octave programs. |
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50 |
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51 @item |
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52 When you encounter an error condition, call the function @code{error} |
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53 (or @code{usage}). The @code{error} and @code{usage} functions do not |
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54 return. |
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55 @xref{Errors}. |
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56 |
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57 @item |
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58 Please put a copyright notice on the file if you give copies to anyone. |
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59 Use the same lines that appear at the top of the function files |
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60 distributed with Octave. If you have not signed papers to assign the |
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61 copyright to anyone else, then place your name in the copyright notice. |
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62 @end itemize |
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63 |
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64 @node Coding Tips |
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65 @section Tips for Making Code Run Faster. |
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66 @cindex execution speed |
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67 @cindex speedups |
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68 |
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69 Here are some ways of improving the execution speed of Octave programs. |
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70 |
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71 @itemize @bullet |
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72 @item |
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73 Avoid looping wherever possible. |
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74 |
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75 @item |
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76 Use iteration rather than recursion whenever possible. |
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77 Function calls are slow in Octave. |
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78 |
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79 @item |
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80 Avoid resizing matrices unnecessarily. When building a single result |
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81 matrix from a series of calculations, set the size of the result matrix |
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82 first, then insert values into it. Write |
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83 |
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84 @example |
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85 @group |
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86 result = zeros (big_n, big_m) |
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87 for i = over:and_over |
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88 r1 = @dots{} |
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89 r2 = @dots{} |
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90 result (r1, r2) = new_value (); |
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91 endfor |
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92 @end group |
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93 @end example |
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94 |
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95 @noindent |
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96 instead of |
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97 |
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98 @example |
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99 @group |
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100 result = []; |
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101 for i = ever:and_ever |
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102 result = [ result, new_value() ]; |
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103 endfor |
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104 @end group |
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105 @end example |
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106 |
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107 @item |
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108 Avoid calling @code{eval} or @code{feval} whenever possible, because |
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109 they require Octave to parse input or look up the name of a function in |
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110 the symbol table. |
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111 |
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112 If you are using @code{eval} as an exception handling mechanism and not |
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113 because you need to execute some arbitrary text, use the @code{try} |
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114 statement instead. @xref{The try Statement}. |
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115 |
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116 @item |
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117 If you are calling lots of functions but none of them will need to |
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118 change during your run, set the variable |
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119 @code{ignore_function_time_stamp} to @code{"all"} so that Octave doesn't |
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120 waste a lot of time checking to see if you have updated your function |
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121 files. |
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122 @end itemize |
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123 |
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124 @node Documentation Tips |
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125 @section Tips for Documentation Strings |
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126 |
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127 Here are some tips for the writing of documentation strings. |
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128 |
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129 @itemize @bullet |
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130 @item |
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131 Every command, function, or variable intended for users to know about |
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132 should have a documentation string. |
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133 |
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134 @item |
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135 An internal variable or subroutine of an Octave program might as well have |
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136 a documentation string. |
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137 |
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138 @item |
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139 The first line of the documentation string should consist of one or two |
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140 complete sentences that stand on their own as a summary. |
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141 |
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142 The documentation string can have additional lines that expand on the |
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143 details of how to use the function or variable. The additional lines |
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144 should also be made up of complete sentences. |
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145 |
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146 @item |
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147 For consistency, phrase the verb in the first sentence of a |
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148 documentation string as an infinitive with ``to'' omitted. For |
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149 instance, use ``Return the frob of A and B.'' in preference to ``Returns |
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150 the frob of A and B@.'' Usually it looks good to do likewise for the |
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151 rest of the first paragraph. Subsequent paragraphs usually look better |
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152 if they have proper subjects. |
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153 |
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154 @item |
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155 Write documentation strings in the active voice, not the passive, and in |
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156 the present tense, not the future. For instance, use ``Return a list |
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157 containing A and B.'' instead of ``A list containing A and B will be |
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158 returned.'' |
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159 |
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160 @item |
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161 Avoid using the word ``cause'' (or its equivalents) unnecessarily. |
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162 Instead of, ``Cause Octave to display text in boldface,'' write just |
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163 ``Display text in boldface.'' |
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164 |
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165 @item |
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166 Do not start or end a documentation string with whitespace. |
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167 |
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168 @item |
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169 Format the documentation string so that it fits in an Emacs window on an |
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170 80-column screen. It is a good idea for most lines to be no wider than |
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171 60 characters. |
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172 |
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173 However, rather than simply filling the entire documentation string, you |
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174 can make it much more readable by choosing line breaks with care. |
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175 Use blank lines between topics if the documentation string is long. |
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176 |
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177 @item |
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178 @strong{Do not} indent subsequent lines of a documentation string so |
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179 that the text is lined up in the source code with the text of the first |
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180 line. This looks nice in the source code, but looks bizarre when users |
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181 view the documentation. Remember that the indentation before the |
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182 starting double-quote is not part of the string! |
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183 |
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184 @item |
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185 The documentation string for a variable that is a yes-or-no flag should |
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186 start with words such as ``Nonzero means@dots{}'', to make it clear that |
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187 all nonzero values are equivalent and indicate explicitly what zero and |
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188 nonzero mean. |
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189 |
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190 @item |
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191 When a function's documentation string mentions the value of an argument |
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192 of the function, use the argument name in capital letters as if it were |
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193 a name for that value. Thus, the documentation string of the operator |
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194 @code{/} refers to its second argument as @samp{DIVISOR}, because the |
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195 actual argument name is @code{divisor}. |
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196 |
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197 Also use all caps for meta-syntactic variables, such as when you show |
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198 the decomposition of a list or vector into subunits, some of which may |
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199 vary. |
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200 @end itemize |
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201 |
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202 @node Comment Tips |
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203 @section Tips on Writing Comments |
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204 |
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205 Here are the conventions to follow when writing comments. |
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206 |
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207 @table @samp |
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208 @item # |
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209 Comments that start with a single sharp-sign, @samp{#}, should all be |
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210 aligned to the same column on the right of the source code. Such |
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211 comments usually explain how the code on the same line does its job. In |
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212 the Emacs mode for Octave, the @kbd{M-;} (@code{indent-for-comment}) |
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213 command automatically inserts such a @samp{#} in the right place, or |
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214 aligns such a comment if it is already present. |
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215 |
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216 @item ## |
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217 Comments that start with two semicolons, @samp{##}, should be aligned to |
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218 the same level of indentation as the code. Such comments usually |
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219 describe the purpose of the following lines or the state of the program |
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220 at that point. |
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221 @end table |
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222 |
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223 @noindent |
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224 The indentation commands of the Octave mode in Emacs, such as @kbd{M-;} |
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225 (@code{indent-for-comment}) and @kbd{TAB} (@code{octave-indent-line}) |
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226 automatically indent comments according to these conventions, |
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227 depending on the number of semicolons. @xref{Comments,, |
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228 Manipulating Comments, emacs, The GNU Emacs Manual}. |
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229 |
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230 @node Function Headers |
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231 @section Conventional Headers for Octave Functions |
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232 @cindex header comments |
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233 |
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234 Octave has conventions for using special comments in function files |
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235 to give information such as who wrote them. This section explains these |
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236 conventions. |
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237 |
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238 The top of the file should contain a copyright notice, followed by a |
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239 block of comments that can be used as the help text for the function. |
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240 Here is an example: |
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241 |
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242 @example |
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243 ## Copyright (C) 1996, 1997 John W. Eaton |
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244 ## |
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245 ## This file is part of Octave. |
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246 ## |
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247 ## Octave is free software; you can redistribute it and/or |
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248 ## modify it under the terms of the GNU General Public |
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249 ## License as published by the Free Software Foundation; |
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250 ## either version 2, or (at your option) any later version. |
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251 ## |
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252 ## Octave is distributed in the hope that it will be useful, |
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253 ## but WITHOUT ANY WARRANTY; without even the implied |
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254 ## warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR |
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255 ## PURPOSE. See the GNU General Public License for more |
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256 ## details. |
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257 ## |
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258 ## You should have received a copy of the GNU General Public |
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259 ## License along with Octave; see the file COPYING. If not, |
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260 ## write to the Free Software Foundation, Inc., 51 Franklin Street, |
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261 ## Fifth Floor, Boston, MA 02110-1301, USA. |
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262 |
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263 ## usage: [IN, OUT, PID] = popen2 (COMMAND, ARGS) |
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264 ## |
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265 ## Start a subprocess with two-way communication. COMMAND |
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266 ## specifies the name of the command to start. ARGS is an |
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267 ## array of strings containing options for COMMAND. IN and |
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268 ## OUT are the file ids of the input and streams for the |
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269 ## subprocess, and PID is the process id of the subprocess, |
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270 ## or -1 if COMMAND could not be executed. |
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271 ## |
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272 ## Example: |
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273 ## |
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274 ## [in, out, pid] = popen2 ("sort", "-nr"); |
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275 ## fputs (in, "these\nare\nsome\nstrings\n"); |
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276 ## fclose (in); |
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277 ## while (isstr (s = fgets (out))) |
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278 ## fputs (stdout, s); |
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279 ## endwhile |
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280 ## fclose (out); |
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281 @end example |
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282 |
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283 Octave uses the first block of comments in a function file that do not |
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284 appear to be a copyright notice as the help text for the file. For |
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285 Octave to recognize the first comment block as a copyright notice, it |
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286 must start with the word `Copyright' after stripping the leading |
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287 comment characters. |
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288 |
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289 After the copyright notice and help text come several @dfn{header |
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290 comment} lines, each beginning with @samp{## @var{header-name}:}. For |
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291 example, |
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292 |
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293 @example |
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294 @group |
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295 ## Author: jwe |
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296 ## Keywords: subprocesses input-output |
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297 ## Maintainer: jwe |
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298 @end group |
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299 @end example |
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300 |
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301 Here is a table of the conventional possibilities for @var{header-name}: |
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302 |
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303 @table @samp |
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304 @item Author |
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305 This line states the name and net address of at least the principal |
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306 author of the library. |
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307 |
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308 @smallexample |
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309 ## Author: John W. Eaton <jwe@@bevo.che.wisc.edu> |
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310 @end smallexample |
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311 |
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312 @item Maintainer |
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313 This line should contain a single name/address as in the Author line, or |
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314 an address only, or the string @samp{jwe}. If there is no maintainer |
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315 line, the person(s) in the Author field are presumed to be the |
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316 maintainers. The example above is mildly bogus because the maintainer |
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317 line is redundant. |
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318 |
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319 The idea behind the @samp{Author} and @samp{Maintainer} lines is to make |
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320 possible a function to ``send mail to the maintainer'' without |
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321 having to mine the name out by hand. |
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322 |
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323 Be sure to surround the network address with @samp{<@dots{}>} if |
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324 you include the person's full name as well as the network address. |
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325 |
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326 @item Created |
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327 This optional line gives the original creation date of the |
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328 file. For historical interest only. |
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329 |
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330 @item Version |
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331 If you wish to record version numbers for the individual Octave program, |
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332 put them in this line. |
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333 |
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334 @item Adapted-By |
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335 In this header line, place the name of the person who adapted the |
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336 library for installation (to make it fit the style conventions, for |
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337 example). |
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338 |
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339 @item Keywords |
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340 This line lists keywords. Eventually, it will be used by an apropos |
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341 command to allow people will find your package when they're looking for |
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342 things by topic area. To separate the keywords, you can use spaces, |
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343 commas, or both. |
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344 @end table |
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345 |
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346 Just about every Octave function ought to have the @samp{Author} and |
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347 @samp{Keywords} header comment lines. Use the others if they are |
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348 appropriate. You can also put in header lines with other header |
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349 names---they have no standard meanings, so they can't do any harm. |
