Editing Guard (computer science) (section)

=== Flatter code with less nesting ===
The guard provides an [[early exit]] from a [[subroutine]], and is a commonly used deviation from [[structured programming]], removing one level of nesting and resulting in flatter code:<ref name="beck">{{cite book |title=Smalltalk Best Practice Patterns, |first=Kent |last=Beck |authorlink=Kent Beck |year=1997 |section=Guard Clause |pages=178–179}}</ref> replacing <code>if guard { ... }</code> with <code>if not guard: return; ...</code>.

Using guard clauses can be a [[refactoring]] technique to improve code. In general, less nesting is good, as it simplifies the code and reduces cognitive burden.

For example, in [[Python (programming language)|Python]]:

<syntaxhighlight lang="python">
# This function has no guard clause
def f_noguard(x):
    if isinstance(x, int):
        #code
        #code
        #code
        return x + 1
    else:
        return None

# Equivalent function with a guard clause. Note that most of the code is less indented, which makes it easier to read and reason about
def f_guard(x):
    if not isinstance(x, int):
        return None
    #code
    #code
    #code
    return x + 1
</syntaxhighlight>

Another example, written in [[C (programming language)|C]]:

<syntaxhighlight lang="c">
// This function has no guard clause
int funcNoGuard(int x) {
  if (x >= 0) {
    //code
    //code
    //code
    return x + 1; 
  } else {
    return 0;
  }
}

// Equivalent function with a guard clause
int funcGuard(int x) {
  if (x < 0) {
    return 0;
  }

  //code
  //code
  //code
  return x + 1; 
}
</syntaxhighlight>