Add default values

[jimmykodes]

This will allow specifying a default value to be used in the case that none of the key options are found in the env.

[hinshun]

Hi @jimmykodes, thanks for the PR!

I see that you decided to pick || as the sentinel value to define the default value. Looking around at other struct tags for ideas, it looks like json uses commas to delimit options like omitempty. e.g. json:"myField,omitempty"

Could you change this so it follows this convention, and allows more options in the future? I'd like to see: env:"MY_ENV,default=myValue"

[hinshun]

Also looks pretty similar to: #5

[jimmykodes]

@hinshun Thanks for the feedback!

I've updated things to use default= instead of ||. and, as you pointed out the similarity w/ #5, i've opted to include the required field here as well.

I've chosen to handle required by using required=true|false I understand this is a diversion from something like json:"omitempty" but this implementation allowed it to fit nicely in my switch statement and i also felt doing something like env:"required" would be ambiguous as to whether the field should be required or if that is the name of the env var to look for. Hope that all makes sense.

While i'm here, if you have any other extra tag behaviors you'd like to see added, i'd be happy to take a crack at them.

[hinshun]

Looks very close 👍. Actually, for json struct tags json:",omitempty" is how they disambiguate between the field name and options. I would prefer env:",required" to match this convention.

[jimmykodes]

That solves the ambiguity for a single value, but does not solve a case like this: env:"REQUIRED,required" where required could be a key to lookup or marking the field required. If you consider this ambiguity to be acceptable, let me know and i'll get that updated.

A possible alternate solution i see would be to structure tags like env:all,the,env,keys;default=val,required where all the possible env var keys are on the left of the semicolon and all option arguments would be on the right.

either way, lemme know what you would prefer.

[hinshun]

You're right, I haven't thought of the multiple env keys. Let's just stick with your current implementation then.