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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