How to Iterate Through Parallel Arrays in HTML/Template using the `index` Function?

Iterating Parallel Arrays in HTML/Template Using Index

Many development scenarios involve working with parallel arrays, where two or more arrays have the same size and their elements should be accessed in a synchronized manner. Understanding how to iterate through these parallel arrays becomes crucial in such situations.

Question:

How can index within a range block be used to iterate through parallel arrays in HTML/Template?

Failed Attempt:

This code fails to achieve the desired result:

{{range $i, $e := .First}}$e - {{index .Second $i}}{{end}}

Solution:

The key to succeeding here is leveraging the index function, a predefined global template function in HTML/Template. It allows indexing of the first argument by subsequent arguments.

index   Returns the result of indexing its first argument by the following arguments. Thus index x 1 2 3 is, in Go syntax, x[1][2][3]. Each indexed item must be a map, slice, or array.

The initial code fails because it does not account for the reassignment of dot within the range block. To access the original dot, we can utilize another predefined template function:

When execution begins, $ is set to the data argument passed to Execute, that is, to the starting value of dot.

An improved version of the code becomes:

{{range $i, $e := .First}}$e - {{index $.Second $i}}{{end}}

Alternative Approach:

Consider a cleaner approach by defining a custom template function called zip. This function takes multiple slices as input and generates a slice of pairs, one for each corresponding element in the input slices. It can then be used in the template to simplify the iteration process.

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