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What is software complexity
and how can you manage it?
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Carl Alexander
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@twigpress
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carlalexander.ca
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No content
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“How did this happen? How did
this code get so messy?”
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Culprit is software complexity
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Not a topic that we’re familiar
with when we start coding
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Focused on
creating code that works
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Not thinking
about maintaining it
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Software complexity
makes this hard
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What is software complexity?
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Complexity is a measurement
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How much does your code
interact with other code?
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Multiple ways to measure this
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Cyclomatic complexity
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Better-known complexity
measurement method
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Measures the number of
"linearly independent paths"
through a piece of code
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function insert_default_value($mixed)
{
if (empty($mixed)) {
$mixed = 'value';
}
return $mixed;
}
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function insert_default_value($mixed)
{
if (empty($mixed)) {
$mixed = 'value';
}
return $mixed;
}
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function insert_default_value($mixed)
{
if (empty($mixed)) {
$mixed = 'value';
}
return $mixed;
}
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function insert_default_value($mixed)
{
if (empty($mixed)) {
$mixed = 'value';
}
return $mixed;
}
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Use control flow graph to
represents paths in our code
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1
2 3
4
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1 2
3 4
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Cyclomatic complexity equation:
M = E − N + 2
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Cyclomatic complexity equation:
M = 4 − 4 + 2
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1 2
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This is a lot of work!
(Ain’t nobody got time for that!)
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Easy mode calculation
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function insert_default_value($mixed) // 1
{
if (empty($mixed)) { // 2
$mixed = 'value';
}
return $mixed;
}
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function insert_default_value($mixed) // 1
{
if (!is_string($mixed) || empty($mixed)) { // 2,3
$mixed = 'value';
}
return $mixed;
}
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What's a good cyclomatic
complexity value?
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Low complexity
(1 - 4)
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Moderate complexity
(5 - 7)
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High complexity
(8 - 10)
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“Ludicrous!” complexity
(10+)
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Issues with
cyclomatic complexity
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Treats if, while, for and case
statements as identical
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A for loop is the same
the 1st or 10,000th time
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An if statement alters
the path through your code
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Different effect on complexity
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Doesn't account for nesting
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Is nested for loops
the same as linear for loops?
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Cognitive complexity
not taken into consideration
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NPATH
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Solves the shortcomings of
cyclomatic complexity
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Counts the number of “acyclic
execution paths” in your code
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Counts the number of
“unique paths” in your code
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function insert_default_value($mixed)
{
if (!is_string($mixed) || empty($mixed)) {
$mixed = 'value';
}
return $mixed;
}
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How many unique paths
does our function have?
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Easy to visualize so far!
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function insert_default_value($mixed)
{
if ($mixed instanceof ToStringInterface) {
$mixed = $mixed->to_string();
}
if (!is_string($mixed) || empty($mixed)) {
$mixed = 'value';
}
return $mixed;
}
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function insert_default_value($mixed)
{
if ($mixed instanceof ToStringInterface) {
$mixed = $mixed->to_string();
}
if (!is_string($mixed) || empty($mixed)) {
$mixed = 'value';
}
return $mixed;
}
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How many paths are there now?
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(Answer: 6)
How many paths are there now?
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Statements are multiplicative
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2 * 3 = 6
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Conditionals are dangerous
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Unique paths increase quickly
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Rarely have two conditionals
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What if we had a dozen?
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What if we had a dozen?
(2¹² = 4096 unique paths!)
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How many unique paths
should your code have?
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Tools warn you at 200 paths
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50 paths is more reasonable
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How to reduce complexity
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Break your large function or
method into smaller ones
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Example:
Going from 12 to 6 statements
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Example:
Going from 12 to 6 statements
(4096 => 2⁶ = 64 unique paths)
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Not easy to split
functions or methods in two
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More common to extract
small blocks of code
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What code is good to extract?
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Easiest is code that logically
belongs together
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function create_reminder($name, $date = '')
{
// ...
$date_format = 'Y-m-d H:i:s';
$formatted_date = DateTime::createFromFormat($date_format, $date);
if (!empty($date)
&& (!$formatted_date || $formatted_date->format($date_format) != $date)
) {
throw new InvalidArgumentException();
}
// ...
}
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function create_reminder($name, $date = '')
{
// ...
$date_format = 'Y-m-d H:i:s';
$formatted_date = DateTime::createFromFormat($date_format, $date);
if (!empty($date)
&& (!$formatted_date || $formatted_date->format($date_format) != $date)
) {
throw new InvalidArgumentException();
}
// ...
}
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function create_reminder($name, $date = '')
{
// ...
if (!empty($date) && !is_reminder_date_valid($date)) {
throw new InvalidArgumentException();
}
// ...
}
function is_reminder_date_valid($date)
{
$date_format = 'Y-m-d H:i:s’;
$formatted_date = \DateTime::createFromFormat($date_format, $date);
return $formatted_date && $formatted_date->format($date_format) === $date;
}
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function create_reminder($name, $date = '')
{
// ...
if (!empty($date) && !is_reminder_date_valid($date)) {
throw new InvalidArgumentException();
}
// ...
}
function is_reminder_date_valid($date)
{
$date_format = 'Y-m-d H:i:s';
$formatted_date = \DateTime::createFromFormat($date_format, $date);
return $formatted_date && $formatted_date->format($date_format) === $date;
}
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Large conditional statements
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function send_response(array $response)
{
if (empty($response['headers'])
|| !is_array($response['headers'])
|| empty($response[‘headers']['status'])
) {
throw new \InvalidArgumentException();
}
// ...
}
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function send_response(array $response)
{
if (empty($response['headers'])
|| !is_array($response['headers'])
|| empty($response[‘headers']['status'])
) {
throw new \InvalidArgumentException();
}
// ...
}
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function send_response(array $response)
{
if (!response_has_status_header($response)) {
throw new \InvalidArgumentException();
}
// ...
}
function response_has_status_header(array $response)
{
return !empty($response['headers'])
&& is_array($response['headers'])
&& !empty($response['headers']['status']);
}
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function send_response(array $response)
{
if (!response_has_status_header($response)) {
throw new \InvalidArgumentException();
}
// ...
}
function response_has_status_header(array $response)
{
return !empty($response['headers'])
&& is_array($response['headers'])
&& !empty($response['headers']['status']);
}
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Combining conditionals together
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function insert_default_value($mixed)
{
if ($mixed instanceof ToStringInterface) {
$mixed = $mixed->to_string();
}
if (!is_string($mixed) || empty($mixed)) {
$mixed = 'value';
}
return $mixed;
}
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function insert_default_value($mixed)
{
if ($mixed instanceof ToStringInterface) {
$mixed = $mixed->to_string();
} elseif (!is_string($mixed) || empty($mixed)) {
$mixed = 'value';
}
return $mixed;
}
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function insert_default_value($mixed)
{
if ($mixed instanceof ToStringInterface) {
$mixed = $mixed->to_string();
} elseif (!is_string($mixed) || empty($mixed)) {
$mixed = 'value';
}
return $mixed;
}
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Are we just hiding the problem?
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Evaluating the complexity of a
function or method
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Not evaluating the complexity of
the software as a whole
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Correlation between the two
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Tools
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Calculating complexity values
isn’t practical
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Tools needed to scan your code
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Command-line tools
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Good starting point
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PHP code sniffer
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Enforces coding standards
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Includes cyclomatic complexity
(But not NPATH)
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PHP mess detector
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Detects problems in your code
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Supports both
measurement methods
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Consider using both
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Code quality services
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Good for teams
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Connects to your git repository
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Continuously analyzes your code
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Enforces code quality
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Codacity
Code Climate
Scrutinizer
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Complexity isn't that complex
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Intimidating topic
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Theory and language
make it seem complicated
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All about the size of your
functions and methods
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Mathematics only there to
quantify the effect
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Not necessary
to reduce complexity
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Just focus on keeping your
functions and methods small
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Thank you!