When and Why Use Pointers to Pointers in Your Code?

Pointers to Pointers: Practical Applications

Pointers to pointers, such as int, offer unique capabilities in programming, enabling one to alter the reference of a variable instead of just its contents. While this concept may seem abstract, it finds practical applications in specific scenarios.

In the context of function parameters, pointers to pointers excel. A function that needs to modify the target of a variable can employ a struct pointer, allowing the function to adjust which object the variable references. For example, in the Go compiler's internals (cmd/compile/internal/gc/racewalk.go), certain functions accept Node parameters. This design allows the function to potentially modify the object pointed to by the variable.

Beyond function parameters, pointers to pointers are also leveraged in languages without multiple return values. By using a **NSError pointer as a final parameter in Objective-C methods, the function can optionally return an error condition.

To provide further examples, consider a function that operates on an HTML page that may or may not have been parsed (github.com/andybalholm/redwood/prune.go). Utilizing a **html.Node pointer enables the function to either reuse an existing tree or parse the page on demand, creating opportunities for efficiency.

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