Support to read tags and values and also set them.

[Abhishek Pande]

It would be nice if we have functionality to read struct tags and also get and set values for respective field.

Thanks.

[Bartłomiej Krukowski]

@adpande I'm not sure how would you see it, could you please draft a pseudocode to describe what you have in mind?

[Abhishek Pande]

Hi @bkrukowski ,

Here is the actual code I used to read config from a NATS KV bucket based on the struct tags and set and return the value.

https://gist.github.com/adpande/99881aef7de899c46916a47e0968825b

Have a look at it. If we make it easy to read struct tags and set values accordingly, it would be a nice feature for this library to add.

Regards,
Abhishek

[Bartłomiej Krukowski]

@adpande hmmm... I believe the most flexible approach would be to manipulate values by callbacks, because tags may have a bit more sophisticated logic, e.g.:

Field int `json:"myName,omitempty"`

in the above example the JSON tag equals myName,omitempty. I drafted how I would see it here #8 (see the ExampleSetByCallback func). Feel free to comment on that PR.

	var person struct {
		Name string `custom:"name"`
		Age  int    `custom:"age"`
	}

	config := map[string]any{
		"name": "Jane",
		"age":  25,
	}

	_ = setter.SetByCallback(
		&person,
		func(field reflect.StructField) (_ interface{}, ok bool) {
			// check whether the given tag exists
			tag, ok := field.Tag.Lookup("custom")
			if !ok {
				return nil, false
			}

			// check whether we have the desired value in the config
			if val, ok := config[tag]; ok {
				return val, ok
			}

			return nil, false
		},
	)