Temporary Field

Also Known As

TL;DR

Explanation

Temporary Field is a smell where an instance variable is only populated during part of the object's lifecycle — set before a complex operation and ignored at all other times. Readers must understand when the field is valid and when it isn't, adding cognitive load. The refactoring is usually Extract Class: move the temporary fields and the methods that use them into a dedicated parameter object or method object, making the state explicit and scoped.

Common Misconception

Why It Matters

Common Mistakes

• Setting instance properties only inside specific methods and using them elsewhere without null checks.
• Using $this->result as a temporary accumulator in a method instead of a local variable or return value.
• Not noticing temporary fields because they are null-initialised — the null hides the pattern.
• Fixing temporary fields by adding null checks everywhere rather than eliminating the temporary nature.

Code Examples

// Field only meaningful during one operation — confuses readers
class OrderProcessor {
    private ?array \$currentItems = null; // only set during process()
    private ?float \$subtotal     = null; // only meaningful mid-calculation

    public function process(Order \$order): void {
        \$this->currentItems = \$order->items;
        \$this->subtotal     = \$this->calculateSubtotal();
        // ...
        \$this->currentItems = null; // reset when done
    }
}

// Move temporary fields to local variables or a parameter object
class OrderProcessor {
    public function process(Order \$order): Invoice {
        \$items    = \$order->items;               // local — scope is clear
        \$subtotal = \$this->calculateSubtotal(\$items);
        return \$this->buildInvoice(\$items, \$subtotal);
    }
}

References

• ↗ https://refactoring.guru/smells/temporary-field

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