Deprecation of ${} Variable Interpolation Syntax in PHP 8.2 and Its Removal in PHP 9

The PHP community approved a proposal—by a single dissenting vote—to deprecate the use of ${} for inserting variables into double‑quoted strings in the upcoming PHP 8.2 release, with the intention of removing the syntax altogether in PHP 9.

Currently PHP allows variable interpolation in double‑quoted strings and heredocs using four forms:

Direct insertion: "$foo"

Brace‑enclosed variable: "{$foo}"

Brace‑enclosed variable with a leading dollar sign: "${foo}"

Variable‑variables syntax: "${expr}" (equivalent to (string) ${expr} )

The proposal’s author, Ilija Tovilo, argues that the first two forms have clear trade‑offs, while the third and fourth are easily confused; the fourth form, in particular, represents true variable‑variables and is rarely used in string contexts.

Analysis of the top 1,000 repositories on Packagegist shows 267 occurrences of the third form and zero occurrences of the fourth, indicating minimal real‑world usage.

Although other languages such as Bash and JavaScript support a ${foo} syntax, their semantics differ: in JavaScript it evaluates arbitrary expressions, while in PHP it creates a variable variable, leading to potential confusion for developers familiar with other ecosystems.

Looking ahead, the author suggests a new syntax like var_dump("{$:func()}") and recommends removing the rarely used forms to avoid further ambiguity.

For full details, refer to the official RFC announcement.