Why Does `json_encode` Treat Sparse Arrays Differently Depending on Their Structure?

JSON_ENCODE Encodes Sparse Arrays Differently: Object vs. Array

When working with sparse arrays, it's important to understand how json_encode behaves. A sparse array is one that contains missing indices, creating gaps in the numerical sequence.

The Issue

As demonstrated in the provided code snippet, json_encode initially encodes the sparse array $a as an array. However, after removing an element using unset, the subsequent json_encode call produces a JSON object.

The Explanation

JSON has no way of representing arrays with missing indices. As a result, json_encode falls back to encoding sparse arrays as JSON objects when it encounters such gaps.

The Solution

To avoid this behavior and ensure that sparse arrays are consistently encoded as arrays, you can use array_values($a) before applying json_encode. This function reindexes the array, removing the gaps and ensuring consistent output.

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