Question 1

How to handle required options in Scallop?

Accepted Answer

Use the 'required' parameter in opt definitions, like opt[Int](required = true). Scallop validates this during verify() and throws an error if missing, ensuring mandatory arguments are enforced.

Question 2

Scallop vs scopt or other Scala CLI parsers?

Accepted Answer

Scallop offers more advanced features like backtracking parsers and nested subcommands, but can be more verbose. Scopt is simpler for basic cases with a more concise API, while Argbridge provides a functional style; choose based on complexity needs.

Question 3

How to parse -D style property arguments with Scallop?

Accepted Answer

Use the props[String]('D') method to define property options, handling arguments like -Dkey=value or -D key1=value key2=value. This is shown in the 'fancy things' example where properties are extracted from a list.

Question 4

Is Scallop good for Scala.js or Native projects?

Accepted Answer

Yes, Scallop supports Scala Native and Scala.js by using the %%% dependency in SBT, as mentioned in the installation section. It's cross-built for these targets, making it versatile for cross-platform CLI tools.

Question 5

How to define default values for options?

Accepted Answer

Use the 'default' method in opt definitions, e.g., opt[Int](default = Some(5)). Scallop will use this value if the option is not provided, simplifying configuration handling without extra validation.

Question 6

What are the performance implications of the backtracking parser?

Accepted Answer

For most CLI applications, performance is adequate, but the backtracking logic in trailing argument matching might add overhead with very complex or ambiguous argument patterns. It prioritizes correctness over speed in edge cases.

scallop

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