svn: /phpdoc/en/trunk/language/ operators.xml

mgf Thu, 09 Jun 2011 07:20:56 +0000 Revision: http://svn.php.net/viewvc?view=revision&revision=311960 Log: Rewrite of Operators intro and tidy up of text around Precedence table. Changed paths: U phpdoc/en/trunk/language/operators.xml Modified: phpdoc/en/trunk/language/operators.xml =================================================================== --- phpdoc/en/trunk/language/operators.xml 2011-06-09 07:16:13 UTC (rev 311959) +++ phpdoc/en/trunk/language/operators.xml 2011-06-09 07:20:56 UTC (rev 311960) @@ -3,25 +3,26 @@ <chapter xml:id="language.operators" xmlns="http://docbook.org/ns/docbook"> <title>Operators</title> <simpara> - An operator is something that you feed with one or more values (or - expressions, in programming jargon) which yields another value (so that the - construction itself becomes an expression). So you can think of functions - or constructions that return a value (like print) as operators and those - that return nothing (like echo) as any other thing. + An operator is something that takes one or more values (or + expressions, in programming jargon) and yields another value (so that the + construction itself becomes an expression). </simpara> <para> - There are three types of operators. Firstly there is the unary operator which - operates on only one value, for example ! (the negation operator) or ++ - (the increment operator). The second group are termed binary operators; this - group contains most of the operators that PHP supports, and a list follows - below in the section <link linkend="language.operators.precedence">Operator - Precedence</link>. + Operators can be grouped according to the number of values they take. Unary + operators take only one value, for example ! (the negation operator) or ++ + (the increment operator). Binary operators take two values, such as the + familiar arithmetical + (plus) and - (minus), and the majority of PHP + operators fall into this category. Finally there is a single ternary + operator, ? :, which takes three values; this is usually referred to simply + as "the ternary operator" (although it should more properly be called the + conditional operator). </para> <para> - The third group is the ternary operator: ?:. It should be used to select - between two expressions depending on a third one, rather than to select two - sentences or paths of execution. Surrounding ternary expressions with - parentheses is a very good idea. + A full list of PHP operators follows in the section + <link linkend="language.operators.precedence">Operator Precedence</link>. + This also explains operator Presedence and Associativity, which govern + exactly how expressions containing several different operators are + evaluated. </para> <sect1 xml:id="language.operators.precedence"> @@ -34,14 +35,18 @@ has a higher precedence than the addition ("+") operator. Parentheses may be used to force precedence, if necessary. For instance: <literal>(1 + 5) * 3</literal> evaluates to - <literal>18</literal>. If operator precedence is equal, left to right - associativity is used. + <literal>18</literal>. </para> <para> - The following table lists the precedence of operators with the - highest-precedence operators listed at the top of the table. Operators - on the same line have equal precedence, in which case their - associativity decides which order to evaluate them in. + When operators have equal precedence, their associativity decides + whether they are evaluated starting from the right, or starting from + the left - see the examples below. + </para> + <para> + The following table lists the operators in order of precedence, with + the highest-precedence ones at the top. Operators on the same line + have equal precedence, in which case associativity decides the order + of evaluation. <table> <title>Operator Precedence</title> <tgroup cols="2"> @@ -208,8 +213,9 @@ </table> </para> <para> - Left associativity means that the expression is evaluated from left to right, - right associativity means the opposite. + For operators of equal precedence, left associativity means that + evaluation proceeds from left to right, and right associativity means + the opposite. <example> <title>Associativity</title> <programlisting role="php"> @@ -229,7 +235,8 @@ ]]> </programlisting> </example> - Use parentheses to increase readability of the code. + Use of parentheses, even when not strictly necessary, can often increase + readability of the code. </para> <note> <para>