How Do Pipelines Work in Go's Template Engine?

Pipelines in Go Template Engine Explained

Go provides two template packages: text/template and html/template. The html/template package focuses on generating HTML output safely against code injection while sharing an interface with text/template. Consequently, the basics of template processing are primarily documented in the text/template package.

Understanding Pipelines

Pipelines refer to sequences of value evaluations within a template. They consist of commands separated by the pipe character '|'. Each command can be a value, a function or method call with its arguments, or a method without arguments when placed at the end of a chain. The result of each command is passed as the last argument to the following command, with the output of the final command representing the pipeline's value.

The Dot (.) Symbol

The dot . is a cursor that points to the current location in the data structure passed to the template. It initially points to the value passed to the template but can be modified by actions like {{range}} or {{with}}.

When using .Name in your template, you are referencing the Name field or method of the value currently pointed to by the dot. If the value is a struct, .Name will access the corresponding field or method at the beginning of the template.

Pipelines in Template Inclusions

When using {{template}}, you specify a pipeline to pass the current dot value to the included template. The value passed as the pipeline becomes the dot inside the invoked template.

Using $ to Access Original Data

As the dot can change during template processing, the $ symbol is provided to access the original value passed to the template execution. This allows you to reach any part of the original value, even within deeply nested template invocations.

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