Product type

As explained in Write Powerful Rust Macros

A product type is a composite type whose possible values are combinations of values from all its component fields.

A product type combines fields, so each possible value contains one value from every component. Structs are the familiar example. The number of possible states equals the product of the fields’ possible values, which can create many combinations to validate. section 7.3

Counting struct states

A struct containing a u8 and a boolean has 256 × 2 = 512 possible states. A value containing 120 and true differs from one containing 119 and true. That flexibility can require conditionals to determine whether a state meets the application’s requirements. section 7.3

Product types belong to algebraic data types and contrast with sum types. Sum types restrict a value to one alternative, making their smaller state space well suited to pattern matching; Rust enums provide this model. section 7.3

Figure 7.2 The myriad of options of a product type versus the simplicity of the sum type

Compare the many combinations available in a product type with the restricted alternatives of a sum type. section 7.3

How Write Powerful Rust Macros covers it

How deep it goes

Defines state multiplication with a worked example, then contrasts product types with sum types without implementing product types.

Examples

Uses a struct containing a u8 and boolean, contrasting values such as 120,true and 119,true.

What you can do after

Evaluate how a struct’s field combinations expand its state space and why validation may require conditionals.

How it connects

Connects product types with structs, algebraic data types, sum types, enums, and pattern matching.

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Also explained in

• 

  liveBookmanning.com
  Functional Design and Architecture: Examples in HaskellA product type combines multiple component values into one composite value, such as a tuple or record.

Compare how 2 books explain product type →

Related concepts

• union typecontrasts with · A union type is a type whose values can be any one of several specified alternative types or variants.
• algebraic data typekind of · An algebraic data type is a composite type whose values are formed from product structures, finite alternatives, or both through type constructors.
• Cartesian productuses · A Cartesian product is the set of all ordered tuples formed by selecting one element from each of multiple sets or sequences.
• anonymous recordincludes · An anonymous record is an F# record value with named fields whose record type is inferred without an explicit named type declaration.
• tupleincludes · A tuple is a finite, ordered collection of elements treated as a single composite value or record.
• recordincludes · A record is a structured data unit or type that groups related values into fields or properties, typically to represent one item, entity, or observation.

This explainer was generated by Manning's knowledge graph from the text of Write Powerful Rust Macros. The section links point to the parts of the book it draws on.