58 lines
2.0 KiB
Plaintext
58 lines
2.0 KiB
Plaintext
---
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title: Enums
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description: Defining algebraic data types with Mist's type-first convention.
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icon: Layers
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---
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Enums in Mist serve as powerful algebraic data types (ADTs), maintaining the exact behavior and safety of Rust enums while applying the language-wide `type name` convention for variants that contain data.
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## Basic Syntax
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An enum can contain unit variants, tuple variants, or struct-like variants. Following Mist's core philosophy, struct-like variants place the type before the identifier.
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```mist
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public enum TaskState {
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Pending,
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InProgress,
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Completed,
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// Struct-like variant using 'type name'
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Failed {
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String reason,
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i32 code,
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},
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}
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```
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## Variant Types
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Mist supports all standard variant shapes, ensuring a 1:1 mapping to the underlying Rust execution model.
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```mist
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enum Message {
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Quit, // Unit
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Move(i32, i32), // Tuple
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Write(String), // Tuple
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ChangeColor { // Struct-like
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u8 r, u8 g, u8 b,
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},
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}
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```
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## Generics & Lifetimes
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Just like structs and functions, enums declare generics and lifetimes in a unified block. This is particularly useful for defining custom Result or Option types that handle references.
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```mist
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public enum Validation<'a, T> {
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Valid(T),
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Invalid {
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str'a* message,
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u32 error_id,
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},
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}
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```
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## Key Characteristics
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- **Consistent Member Declaration**: Struct-like variants maintain the `type name` order, ensuring that data modeling feels identical whether you are defining a top-level `struct` or an `enum` variant.
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- **Rust-Native ADTs**: Enums compile directly to Rust enums, allowing for exhaustive pattern matching and zero-cost abstraction.
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- **Shared Visibility**: The `pub` modifier at the enum level exports all variants for use in other modules, matching Rust's visibility rules for enums.
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- **Comma-Separated Members**: Fields within struct-like variants are separated by commas, mirroring the syntax used in standard Mist structs.
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