Derive Macro Variable 

#[derive(Variable)]
{
    // Attributes available to this derive:
    #[template]
}

Available on crate feature macros only.

Variable Derive Macro Documentation

This procedural macro generates an implementation of the Variable trait for structs, enabling conversion of struct fields into key-value pairs with various naming and casing options.

Struct-Level Attributes

These attributes are applied to the struct definition:

#[template(rename = "name")] or #[template(alias = "name")]

• Purpose: Renames the struct in the generated variable names
• Example:

  #[template(rename = "UserData")]
  struct User {
      // fields...
  }

  Generates variables like UserData.field_name instead of User.field_name

#[template(case = "case_type")]

• Purpose: Sets the naming case for the struct name
• Valid values:

  Case	Example	Conversion Method
  Lower	hello world	to_lowercase()
  Upper	HELLO WORLD	to_uppercase()
  Snake	hello_world	Lowercase with underscores
  Camel	helloWorld	First word lowercase, others capitalized
  Pascal	HelloWorld	All words capitalized
  Kebab	hello-world	Lowercase with hyphens
  ScreamingSnake	HELLO_WORLD	Uppercase with underscores

• Example:

  #[template(case = "pascal")]
  struct user_settings {
      // fields...
  }

  Generates variables with the struct name converted to PascalCase

#[template(case_fields = "case_type")]

• Purpose: Sets default naming case for all fields
• Valid values: Same as case attribute
• Overrides: Can be overridden by field-level case attributes
• Default: snake_case
• Example:

  #[template(case_fields = "scream")]
  struct Config {
      max_size: usize,
  }

  Generates variable name Config.MAX_SIZE

Field-Level Attributes

These attributes are applied to individual struct fields:

#[template(ignore)]

• Purpose: Excludes the field from variable generation
• Example:

  struct Product {
      id: u64,
      #[template(ignore)]
      internal_code: String,
  }

  Only generates variable for id

#[template(rename = "name")] or #[template(alias = "name")]

• Purpose: Renames the field in the generated variable
• Example:

  struct Point {
      #[template(rename = "x-coord")]
      x: f64,
  }

  Generates variable name Point.x-coord

#[template(case = "case_type")]

• Purpose: Sets naming case for this specific field
• Overrides: The struct-level case_fields setting
• Example:

  struct Settings {
      #[template(case = "kebab")]
      max_file_size: usize,
  }

  Generates variable name Settings.max-file-size

Generated Implementation

The macro generates an implementation of the Variable trait that provides:

1. A variables() method returning an iterator of (Cow<str>, String) tuples
2. Proper case conversion according to the specified attributes
3. Field filtering for ignored fields

Example Output

For this input:

#[template(case = "pascal", case_fields = "kebab")]
struct UserProfile {
    #[template(rename = "first-name")]
    first_name: String,
    #[template(ignore)]
    password: String,
    age: u8,
}

The generated implementation would produce variables:

• UserProfile.first-name
• UserProfile.age

Supported Field Types

The macro works with:

• Named fields (standard structs)
• Tuple structs (fields accessed by index)
• Unit structs (treated as a single value)

Error Handling

The macro will error if:

• Applied to non-struct types (enums, unions, etc.)
• Invalid case type is specified
• Attribute syntax is malformed