How Do Pipelines and the Dot (.) Cursor Work in Go Templates?

Golang Template Engine Pipelines: Understanding the Dot and Pipelines

In Go templates, a "pipeline" is a sequence of commands or function calls that process and transform data. It serves as input for the template execution, represented by the dot (.) cursor.

Pipelines

As described in the text/template documentation, a pipeline consists of:

• Arguments: Raw values representing data.
• Method Calls: Invocation of methods on the current value, possibly with arguments.
• Function Calls: Invocation of functions associated with specific names.

Pipelines are chained using the '|' operator, where the output of each command becomes the input for the next. The final output of the pipeline is the result of the last command.

The Dot (.) Cursor

The dot (.) in a template expression denotes the current value being processed. It serves as a pointer to the data structure passed to the template execution. The starting value of the dot is the passed data, but it can be modified by actions like {{range}} or {{with}}.

For instance, if one passes a struct with a field Name, {{.Name}} refers to the Name field of the struct.

Passing Values to Other Templates

When invoking another template using {{template}}, one can specify the value to be passed as input. For example, {{template "test" .}} passes the current value pointed by the dot to the test template. The value becomes the new cursor inside the invoked template.

The Dollar ($) Special Variable

The template package provides the $ special variable, which holds a reference to the original data passed to the template execution. This allows one to access the original value even after the dot has been modified during processing.

In summary, pipelines allow for flexible data transformations within Go templates. The dot (.) cursor represents the current value, and the $ variable provides access to the original data. These concepts are essential for understanding and effectively utilizing Go templates.

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