Validation and conversion

An untyped config stores supported values without a declared field type. A structured config uses its annotations to validate values at runtime. A value already of the declared type can be assigned directly:

>>> from dataclasses import dataclass
>>> from omegaconf import OmegaConf
>>> @dataclass
... class Settings:
...     port: int = 80
>>> cfg = OmegaConf.structured(Settings)
>>> cfg.port = 8080
>>> cfg.port
8080

Conversion to a declared type

OmegaConf 2.3 attempts conversion during assignment to a typed field. For example, assigning a numeric string to an integer field stores an integer:

>>> cfg.port = "9000"
>>> cfg.port
9000

OmegaConf.update(cfg, "port", "9000") applies the same destination validation and conversion. Invalid values raise ValidationError.

Interpolations and unions

An interpolation is resolved when read. A scalar typed destination validates and, when possible, converts the result. II("source") creates ${source} for a typed field without assigning a string in Python source; SI("${source}") is the other static-checker-friendly form.

>>> from omegaconf import II
>>> @dataclass
... class InterpolatedPort:
...     source: str = "8080"
...     port: int = II("source")
>>> cfg = OmegaConf.structured(InterpolatedPort)
>>> cfg.port, cfg.source
(8080, '8080')

In 2.3, this validation is skipped for container node interpolations. A container-typed field can therefore return a value that does not match its annotation:

>>> from typing import Dict
>>> @dataclass
... class NotValidated:
...     source: int = 0
...     mapping: Dict[str, str] = II("source")
>>> cfg = OmegaConf.structured(NotValidated)
>>> cfg.mapping
0

Union branch selection avoids implicit conversion because the intended branch would be ambiguous: a value must match a declared branch. See supported types.

The 2.4 conversion reference explains warnings for implicit assignment conversion, typed container interpolation validation, and the new oc.coerce resolver.