gostructor

Priority = source order

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This is the feature that sets gostructor apart from a merge-everything-into-one-map unmarshaller. A field can be resolvable by several sources at once. There is no priority tag and no global selector — priority is simply the order of the sources you pass to WithSources. The first source that reports a value wins.

To flip which source leads for a whole config, reorder the slice:

// prod: an operator's env override leads; the default is the fallback.
gostructor.Configure(&cfg, gostructor.WithSources(gostructor.Env(), gostructor.Default()))

// dev: the baked-in default leads, so a stray env var is ignored.
gostructor.Configure(&cfg, gostructor.WithSources(gostructor.Default(), gostructor.Env()))

Try it

The priority example sets LOG_LEVEL=debug and TRACE_RATE=1.0 in the environment, then resolves the same struct twice — once with Env, Default (prod) and once with Default, Env (dev). Only the source order differs.

go run ./examples/priority

Output:

[prod] LogLevel=debug TraceRate=1.0
[dev ] LogLevel=info  TraceRate=0.01

Same struct, same env vars — only the WithSources order changed:
  prod trusts the operator's env override; dev pins the local default.

Same struct, same env vars — prod trusts the operator’s env override, dev pins the local default and ignores the stray env vars. The priority decision lives at the call site, not in the tags.

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