How Can I Properly Pass Functions to Go Templates and Handle Potential Errors?

Passing Functions to Golang Templates: Error Handling and Static Analysis

When accessing a function included in a template, you may encounter an error stating that the function is not defined. To resolve this issue, custom functions must be registered before parsing the templates.

Unlike dynamic languages, Go templates are statically analyzable, requiring the parser to distinguish between valid function names and undefined identifiers. To achieve this, functions must be defined before the template is parsed.

Instead of calling template.ParseFiles() directly, you can utilize template.New() to create an undefined template and employ the ParseFiles() method of the template.Template type. This modification would look like the following:

Additionally, ensure that Template.Execute() returns an error, which you can print to identify any issues with output generation:

These modifications will allow you to successfully pass functions to your Golang templates while maintaining the required static analysis for enhanced security and predictability.

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