use variable value as refrence to other variable in Go tepmplate

How can I use value of a variable to reference to another variable in a Go template?

template:

Hello, {{ index $.planet }}!

data:

{ 
"planet": "neptune",
"planet_field": "planet"
}

I need to use planet_field instead of planet in my template, and have neptune printed.

note: i cant change my data structure, the use case is for Prometheus alert templates that only get data by labels.

I'm testing on this website: gotemplate.io (copy/paste the template/data above into that site).

The value of the planet variable can be referenced through planet_field using the index function as follows:

Hello, {{ index . .planet_field }}!

The index function is a Go template function that retrieves the value from a map/slice using its key or index. index . .planet_field looks up the value of the planet key in the data map, which is neptune.

Here's what it looks like:

👆🏻Go Template Preview

For more details on the index function, please see https://pkg.go.dev/text/template