interpolation.md

Interpolation

EnvironmentInterpolator applies environment variable replacement to the merged config array.

Responsibility

• traverse the merged array recursively
• interpolate string values
• leave non-string values unchanged
• throw when required environment variables are missing

Inputs

• merged array<mixed>
• an EnvironmentReaderInterface implementation

Output

• interpolated array<mixed>

Supported Syntax

${VAR}
${VAR:-default}

Behavior

• strings may contain placeholders as the whole value or inline inside larger strings
• defaults are used only when the environment variable is absent
• values remain strings after interpolation
• arrays are traversed recursively

Environment Source

The default reader is PhpEnvironmentReader, which checks:

1. getenv()
2. $_ENV
3. $_SERVER

Constraints

• no expression evaluation
• no implicit type casting
• invalid unresolved placeholder syntax is rejected

Related Documents

• Concepts
• Interpolation usage
• Exceptions