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extend the examples of side effects

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1 parent 15d3de6 commit 35c7849cdfb9bab3c78a0f1bfc659f53b8f6a2b6 @pmjones pmjones committed May 10, 2012
Showing with 21 additions and 14 deletions.
  1. +21 −14 proposed/
@@ -35,16 +35,19 @@ Use only UTF-8 (no BOM) for PHP code. Do not use other character encodings.
A file should *either* declare new symbols (classes, functions, constants,
etc.) and have no other side effects, *or* it should execute logic with side
-effects, but *not* both.
+effects, but *not both*.
The phrase "side effects" means execution of logic not directly related to
-declaring classes, functions, constants, etc., *merely from including the file*.
+declaring classes, functions, constants, etc., *merely from including the
"Side effects" include but are not limited to: generating output, explicit
use of `require` or `include`, connecting to external services, modifying ini
-settings, emitting errors or exceptions, and so on.
+settings, emitting errors or exceptions, modifying global or static variables,
+reading from or writing to a file, and so on.
-An example of a file with side effects:
+The following is an example of a file with both declarations and side effects;
+i.e, an example of what to avoid:
@@ -54,30 +57,34 @@ ini_set('error_reporting', E_ALL);
// side effect: loads a file
include "file.php";
-// declaration (not a side effect)
+// side effect: generates output
+echo "<html>\n";
+// declaration
function foo()
// function body
-An example of a file with no side effects:
+The following example is of a file that contains declarations without side
+effects; i.e., an example of what to emulate:
+// declaration
+function foo()
+ // function body
// conditional declaration is *not* a side effect
-if (! function_exists('foo')) {
- function foo()
+if (! function_exists('bar')) {
+ function bar()
// function body
-// declaration
-function bar()
- // function body

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