Allow a global prefix for config field names

[cbndr]

Hi Jeremy,
I like your config package a lot, minimalist and still covers 99% of the config use cases.

One thing I am missing is using a global prefix for field names. I deploy to k8s and in our environment, a large number of env vars are automatically injected into containers. It is very helpful therefore, to prefix env vars for instance with the app name. Also, with a prefix there is no risk using a prexisting (injected) name. Example:

MYAPP__DATABASE_PORT=5432

Would be used like

var c MyConfig
err := WithPrefix("MYAPP").From("config").FromEnv().To(&c)

Added "WithPrefix" funcs and a test for that.

Best regards, Chris

[JeremyLoy]

HI @cbndr, sorry for the late reply. I did not get an email for some reason. I'll check my settings.

config/example_test.go

Line 30 in d0690ea

os.Setenv("SUBCONFIG__IPWHITELIST", "0.0.0.0 1.1.1.1 2.2.2.2")

Does the above not fit your use case already? If not I'll consider adding another method

[cbndr]

No worries =)
So you are suggesting to encase all config with a struct carrying the name of the app as a work-around?
TBH I'd prefer having a few LOCs for the prefix, as it is also more expressive when reading the code.

[JeremyLoy]

@cbndr I see your point now, I agree there would be a lot of benefit here.

What do you think about having a different To method? I would like to only parse config into memory a single time. So something like this.

builder := config.FromEnv()
configA := builder.ToOverload(&a, "prefixA")
configB := builder.ToOverload(&b, "prefixB")

[cbndr]

Sure, that could work as well. Although I think the method name "ToOverload" is very self-explanatory. On top of that, From() could accept an additional variadic param to allow for an optional prefix.

[JeremyLoy]

Oh haha I didn’t literally mean ToOverload , just wanted to make it clear what it was

I don’t want to mess with From, since that is doing all the parsing. What about adding the variadic arg to To?

[JeremyLoy]

Added in v1.4.0!