Home PHP Function Design

Function Structure

If you have a single function that is very long, break it apart into smaller sub-functions. The definition of "very long" is vague, but often a function longer than 20-30 lines is pushing it.

If you try to describe the function's purpose and find yourself using the word "and" a lot, that probably means the function does too many things and should be split into sub-functions.

Very rarely should you have all of your PHP code outside of a function in a PHP file. It's important to define functions to delegate the significant behaviors of your PHP program. There is no main function in PHP, but it is good practice to write your own "delegator" function to check for things like GET or POST variables and to delegate behavior with functions as appropriate. For small (< 30 lines) PHP programs it is usually appropriate to have only one function, but for longer you should probably have at least two.

Boolean Zen

Don't ever test whether a boolean value is == or != to TRUE or FALSE.

if ($x == TRUE) {
  ...
} else if ($x != TRUE) {
  ...
}

if ($x) {
  ...
} else {
  ...
}

If you have an if/else statement that returns a boolean value based on a test, just directly return the test's result instead.

if ($score1 == $score2) {
  return TRUE;
} else {
  return FALSE;
}

return $score1 == $score2;

If/Else Usage

If/Else Branching Patterns

When using if/else statements, properly choose between various if and else patterns depending on whether the conditions relate to one another. Avoid redundant or unnecessary if tests.

if ($grade >= 90) {
  print("You got an A!");
}
if ($grade >= 80 && $grade < 90) {
  print("You got a B!");
}
if ($grade >= 70 && $grade < 80) {
  print("You got a C!");
}
...

if ($grade >= 90) {
  print("You got an A!");
} else if ($grade >= 80) {
  print("You got a B!");
} else if ($grade >= 70) {
  print("You got a C!");
}
...

If/Else Factoring

Move common code out of if/else statements so that it is not repeated (ie., minimize redundancy in your code).

if ($x < $y) {
  foo();
  $x++;
  print("hi");
} else {
  foo();
  $y++;
  print("hi");
}

foo();
if ($x < $y) {
  $x++;
} else {
  $y++;
}
print("hi");

Loop Usage

For Loops vs. While Loops

Use a for loop when the number of repetitions is known (definite); use a while loop when the number of repetitions is unknown (indefinite).

// repeat exactly size/2 times
for ($i = 0; i < $size / 2; $i++) {
  ...
}

// repeat until $x is <= 0
while ($x > 0) {
  ... // do something with $x
}

Break and Continue

In general, you should avoid break and continue statements unless absolutely necessary. In this class, you should never use these statements (it would be very unlikely you would write code for our assignments in which using one of these would be proper style).

Error Handling

Using `die()` and setting errors with `header`

When handling errors in PHP, you should set the appropriate error code and output the error message using die($msg). die() will cause your program to automatically exit without executing further. If you have several error messages, you may consider factoring them out with an handle_error function.

header("HTTP/1.1 400 Invalid Request");
die("Invalid mode: {$mode}. Please pass modes of 'add' or 'remove'.");

Handling Exceptions with `try/catch`

You may use try/catch statements to handle exceptions as long as you do so without deviating from clean and logical program flow. You should also output the appropriate error messages when catching errors.

function handle_error($msg, $ex) {
  header("Content-Type: text/plain"); # Set 400 code if 400-type error
  print("{$msg}\n");
  die("Error details: {$ex} \n");
}

... 
try {
  # some success code
} catch (PDOException $ex) {
  handle_error("Error adding product into database. Please try again later.", $ex);
}