> ## Documentation Index
> Fetch the complete documentation index at: https://docs.syntblaze.com/llms.txt
> Use this file to discover all available pages before exploring further.
# PHP Short Ternary
The `?:` operator, formally the shorthand ternary operator and colloquially known as the Elvis operator, performs a boolean truthiness check on its left operand. It returns the left operand if it evaluates to `true`, and the right operand if the left operand evaluates to `false`.
```php theme={"dark"}
$result = $expression1 ?: $expression2;
```
## Evaluation Mechanics
1. **Boolean Conversion:** PHP implicitly casts `$expression1` to a boolean.
2. **Short-circuiting:** If `$expression1` is truthy, it is immediately returned. `$expression2` is never evaluated, preventing any side effects associated with it.
3. **Single Evaluation:** Unlike the standard ternary operator where the condition is repeated (`$expr ? $expr : $alt`), the Elvis operator evaluates `$expression1` exactly once.
## Syntactic Equivalence
The Elvis operator is strictly equivalent to the standard ternary operator, with the middle expression omitted:
```php theme={"dark"}
// Shorthand
$result = $expression1 ?: $expression2;
// Standard Ternary Equivalent
$result = $expression1 ? $expression1 : $expression2;
```
## Falsy Triggers
Because the operator relies on PHP's standard type juggling for boolean evaluation, `$expression2` will be returned if `$expression1` resolves to any of the following falsy values:
* `false` (boolean)
* `0` (integer) or `0.0` (float)
* `""` (empty string) or `"0"` (string zero)
* `[]` (empty array)
* `null`
## Error Handling and Undefined Variables
The `?:` operator does not suppress diagnostic errors for undefined variables or array keys. If `$expression1` references a variable that does not exist, PHP will throw an `E_WARNING` (or `E_NOTICE` in PHP \< 8.0) before evaluating the expression as `null` (falsy) and returning `$expression2`.
## Contrast with Null Coalescing (`??`)
It is critical to distinguish `?:` from the null coalescing operator (`??`), as their evaluation criteria differ:
* `?:` evaluates based on **truthiness** (fails on `0`, `""`, `false`, `null`, etc.).
* `??` evaluates based on **existence and non-nullity** (fails *only* on `null` or undefined variables, suppressing undefined warnings).
```php theme={"dark"}
$var = "0";
$a = $var ?: "default"; // Returns "default" (because "0" is falsy)
$b = $var ?? "default"; // Returns "0" (because "0" is not null)
```
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