Struct VecHeader

#[repr(C)]
pub struct VecHeader {
    pub capacity: u16,
    pub element_count: u16,
    pub element_size: u32,
    pub padding: u32,
}

Fields

capacity: u16

Do not change the order of the fields!

Keep the capacity field at the start of the header for consistency across all container types. Placing it first simplifies copy operations: we can verify and preserve capacity before copying the remainder of the header in one contiguous operation.

element_count: u16

Number of live (active) elements currently stored in the collection.

Always located at offset 2, enabling:

• Logical size: Represents the number of valid elements in use.
• Bounds checking: Index and assignment checks (0 <= idx < element_count) can load this field in a single instruction.
• Iteration: Iterators read this field to determine the end of the collection.
• ABI stability: External tools, debuggers, and serializers can consistently locate capacity and element_count across all container types.

element_size: u32

padding: u32

Trait Implementations

impl Clone for VecHeader

fn clone(&self) -> VecHeader

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for VecHeader

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Copy for VecHeader