How to Display Array Indices Starting from 1 in Go Templates?

Understanding Arithmetic in Go Templates

When dealing with arrays in Go templates, the range action allows for iterating through elements along with their zero-based indices. While it's a common practice, the question arises when attempting to display indices that start from 1 instead of 0.

Attempting Direct Arithmetic

An initial effort to add 1 to the index via the expression {{$index 1}} fails, resulting in an "illegal number syntax: " " error." This highlights the lack of built-in arithmetic operations within templates.

Custom Function Approach

To overcome this limitation, it's necessary to create a custom function that handles the arithmetic. In the provided code snippet:

1. A function map is defined with a custom function called "inc."
2. The "inc" function takes an integer as input and returns the incremented value.
3. The function map is passed to the template.Parse() method to register the custom function.
4. Within the template, the custom function "inc" can be used as {{inc $index}} to add 1 to the index during iteration.

In conclusion, while Go templates do not support direct arithmetic operations, creating custom functions like the "inc" function allows for more flexible processing and manipulation of values in templates. This approach provides a robust and customizable solution for handling arithmetic calculations in your Go templates.

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