Derives: Copying and Default (Reference)

This page documents Clone, Copy, and Default, plus field defaults in constructors.

See also:

• Derives & traits

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Clone

• Enables: .clone()
• Meaning: explicit duplication

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Copy

• Meaning: marker trait for implicit copying
• Intended use: small value types (no heap ownership)

Copy vs Clone (rule of thumb):

Trait	Copy happens when	Use for
Clone	you call .clone()	any type
Copy	assignment/pass-by-value	small, simple value types

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Field defaults (construction)

Field defaults are written on fields:

model Settings:
    theme: str = "dark"
    font_size: int = 14

Rules:

• If a field has a default, you may omit it in construction and the default is used.
• If a field has no default, it must be provided when constructing the type.

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Default

• Enables: Type.default()
• Semantics:
• fields with explicit defaults use those defaults
• otherwise, the default of the field type is used

Common type defaults:

Type	Default
int	0
float	0.0
bool	false
str	""
List[T]	[]
Dict[K, V]	{}
Set[T]	set()
Option[T]	None