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Structural Versus Nominal Type System

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The terms "structural type system" and "nominal type system" refer to different approaches used in programming languages to determine type compatibility and relationships between types.

  1. Nominal Type System:

    • In a nominal type system, types are explicitly declared and identified by their names or labels.
    • Type compatibility is determined based on the names or labels of the types, regardless of their structure or content.
    • Types with different names, even if their structures are identical, are considered distinct and incompatible.
    • Examples of languages with nominal type systems include Java and C#. In these languages, explicit type declarations are required, and types are compared based on their declared names.

  2. Structural Type System:

    • In a structural type system, types are based on their actual structure or shape, rather than explicit names or labels.
    • Types are considered compatible if they have the same structure, regardless of whether they are explicitly declared as the same type.
    • Types with different names but the same structure are treated as compatible in a structural type system.
    • Languages like TypeScript and OCaml incorporate structural typing, allowing for more flexibility and code reuse based on the structure of types.

References

  1. Benjamin C. Pierce: "Types and Programming Languages"

    • This is a comprehensive and widely used book that covers the theory and practice of type systems in programming languages. It's suitable for both beginners and those with more advanced knowledge.

  2. Michael L. Scott: "Programming Language Pragmatics"

    • This book provides a broad overview of programming languages, including discussions on type systems and their role in language design. It covers both theoretical concepts and practical considerations.

  3. David A. Schmidt: "Types and Programming Constructs"

    • Schmidt's book is focused on the role of types in programming languages and how they influence the design and implementation of software. It covers both traditional and modern type systems.

  4. Robert Harper: "Practical Foundations for Programming Languages"

    • Harper's book delves into the theoretical foundations of programming languages, including type systems. It's a more advanced text that explores topics such as formal semantics and type theory.

  5. Luca Cardelli: "Types in Programming Languages"

    • This classic paper by Luca Cardelli provides a foundational overview of types in programming languages. It's a good starting point for understanding the fundamental concepts.

  6. Benjamin C. Pierce: "Advanced Topics in Types and Programming Languages"

    • This collection of essays explores advanced topics related to types and programming languages. It's a sequel to Pierce's "Types and Programming Languages" and provides deeper insights into various aspects of type systems.

  7. Dan Grossman: Online Resources: Stanford University course "Programming Languages"

    • This Stanford University course covers type systems and programming languages. You can find lecture videos and materials on platforms like YouTube or the course's official website.