Proposal: Extended Table Syntax with Context or Profile Prefixes

[cheungxiongwei]

Proposal: Extended Table Syntax with Context or Profile Prefixes

Summary

I would like to propose an extended table syntax for TOML that allows contextual or environment-specific sections, using a colon (:) to express inheritance or specialization.

Motivation

In many configuration scenarios (e.g., application environments like development, test, production), it is common to define a base configuration and override only a few fields for each environment.
Currently, TOML does not have a direct way to express “derived” or “contextual” tables, which leads to redundant configuration blocks or requires additional logic in the parser.

Proposed Syntax

Example:

[database]
host = "localhost"
port = 3306
username = "admin"
password = "123456"

[development:database]
debug = true

[test:database]
host = "test-db.example.com"  # override host
debug = false

Semantics

• The base table [database] defines default fields.
• The prefixed tables [development:database], [test:database], etc. represent derived or context-specific configurations.
• When parsed, they can conceptually “extend” the base [database] table, overriding or adding keys.
• A parser or tool could choose to interpret this as a hierarchical configuration, e.g.:

{
  "database": {
    "host": "localhost",
    "port": 3306,
    "username": "admin",
    "password": "123456"
  },
  "development": {
    "database": {
      "host": "localhost",
      "port": 3306,
      "username": "admin",
      "password": "123456",
      "debug": true
    }
  },
  "test": {
    "database": {
      "host": "test-db.example.com",
      "port": 3306,
      "username": "admin",
      "password": "123456",
      "debug": false
    }
  }
}

Benefits

• Reduces duplication in environment-based configuration files.
• Keeps TOML syntax clean and readable.
• Enables consistent hierarchical configuration management.

Alternatives

• Using separate files per environment (e.g., config.dev.toml, config.test.toml).
• Using table arrays or dotted keys (which are less intuitive for inheritance).

Discussion

The colon syntax could be discussed further — alternative separators like /, . or @ may also be considered.
Backward compatibility is maintained since : is currently not allowed in bare keys, so this would not conflict with existing TOML syntax.