This question already has an answer here:
I used go build to generate files. But I can only generate main, which mean go build main.go works while go build dao.go does not generate anything?
How can I generate dao?
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From go help build:
When the command line specifies a single main package,
build writes the resulting executable to output.
Otherwise build compiles the packages but discards the results,
serving only as a check that the packages can be built.