Accessing Parent Pipeline within Range in Template Actions

In Go templates, it's common to use range pipelines to iterate through slices or maps. However, a frequent problem arises when trying to access data outside the immediate scope of the pipeline. This article explores how to achieve this.

Using the $ Variable (Recommended)

The text/template documentation specifies that when execution begins, the $ variable references the data argument passed to Execute. This means we can access the outer scope data by using $.variable.

For example, consider this template:

const page = `{{range .Files}}{{end}}`

Here, .Files refers to a slice of files, but we want to access the Path of the enclosing scriptFiles struct. Using $.Path allows us to do that.

Using a Custom Variable (Legacy Method)

An alternative method involves creating a custom variable to pass into the range scope, as demonstrated in this template:

const page = `{{$p := .Path}}{{range .Files}}{{end}}`

By setting $p to .Path before the range pipeline, we can access the path within the pipeline.

Note: The $ variable method is recommended as it's the more concise and idiomatic approach in current Go versions.