Lazy Construction

Tutorial: First Steps, Nested CompositionSee also: Lie-Typing, API: language

Eager vs Lazy

# Eager: object exists now, no config possible
model = nn.Linear(784, 10)

# Lazy: DictConfig exists now, object constructed on demand
model_cfg = L.call(nn.Linear)(in_features=784, out_features=10)
model = laco.instantiate(model_cfg)

The lazy version can be serialized, overridden, merged, and reproduced.

L.call

L.call(target, *, strict=True, convert="none", recursive=True, **meta)

Returns a callable that accepts keyword arguments and produces a DictConfig.

The wire format is a Hydra-compatible dict:

_target_: torch.nn.Linear
in_features: 784
out_features: 10

strict=True (default): validates kwargs against the target's signature at config-construction time, catching typos before training starts.

strict=False: disables validation, useful for C-extension targets whose signatures cannot be introspected.

convert: controls how Hydra converts structured configs on instantiation. Defaults to "none" (preserve DictConfig wrappers).

recursive: if True (default), Hydra recursively instantiates nested _target_ nodes.

L.partial

optimizer_cfg = L.partial(torch.optim.Adam)(lr=1e-3)
optimizer = laco.instantiate(optimizer_cfg)
# optimizer is functools.partial(Adam, lr=1e-3)
optimizer_with_params = optimizer(params=model.parameters())

Equivalent to L.call but sets _partial_: true in the wire format, so laco.instantiate returns a functools.partial rather than calling the target.

Common pattern: store the partial in the config; bind params= at training time.

L.just

node = L.just(42)
laco.instantiate(node)  # → 42

Wraps an already-constructed value in a DictConfig so it survives serialization. Serializes to a _target_: laco.ops.identity node.

Note: non-serializable objects (tensors, file handles) will fail on laco.dump. For those, store a path or descriptor instead.

L.required[T]()

@L.params
class hps:
    vocab_size: int = L.required[int]()

Produces the OmegaConf MISSING sentinel (??? in YAML). Accessing an unset required field raises MissingMandatoryValue. The generic subscript [int] is for the type-checker; it has no runtime effect.

laco.instantiate

result = laco.instantiate(cfg)

Thin wrapper around hydra.utils.instantiate. Honors all Hydra knobs (_target_, _args_, _partial_, _convert_, _recursive_).

Primitive top-level values (int, float, str, bool, None, set, frozenset, bytes, type, functions) are returned unchanged: callers do not need to check the type before passing a leaf.

LACO_TRACE=1 logs the full config tree before each instantiation.

Cyclic configuration graphs raise LacoCycleError. See API: instantiate.