Why Does PHP Concatenation Seem to Prioritize Over Addition in This Case?

PHP's Conundrum: The Interplay of Addition and Concatenation

PHP developers may encounter peculiar behavior when combining the addition ( ) and concatenation (.) operators. Consider the following code:

<code class="php">$a = 1;
$b = 2;

echo "sum: " .  $a + $b;
echo "sum: " . ($a + $b);</code>

Executing this code produces the following output:

2
sum: 3

Why does the first echo fail to print "sum:"?

Operator Precedence and Associativity

Both the addition and concatenation operators have the same operator precedence. However, they are left associative, meaning they evaluate from left to right. This results in the following evaluation order:

echo "sum:" . ($a + $b); // Parentheses force addition first
echo "sum:" . $a + $b; // Addition performed before concatenation

Numeric Context Conversion

In the second line, where parentheses are used, addition is performed first. However, in the first line, concatenation takes precedence, resulting in:

"sum: 1" + 2

In a numeric context, PHP converts the string "sum: 1" to an integer, resulting in 1. This numeric addition yields the result 2.

Documentation and Implications

This behavior is not explicitly documented in PHP manuals. However, it is crucial to understand the operator precedence and associativity rules when using multiple operators in a single statement. Failure to do so can lead to unexpected results, as demonstrated in this example.

Therefore, it is recommended to use parentheses explicitly to enforce the desired order of operations, particularly when combining different operator types.

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