silk/layout

Checked size-and-alignment descriptions used to request storage from an allocator.

When to use

Prefer of when storage will hold a known Silk type. Use make only at an untyped boundary that already knows a byte size and alignment, and repeat when sizing contiguous elements.

Details

Alignments are non-zero powers of two. repeat preserves the element alignment and reports LayoutOverflow instead of wrapping the aggregate byte size. A Layout describes storage; it does not allocate or initialize it.

Examples

Size storage for repeated values

import silk.layout as Layout

import silk.usize as usize

pub fn main() -> i32 {
  let element = Layout.of<i32>()
  return match move Layout.repeat(move element, 3) {
    Layout.Layout {bytes, alignment} => usize.toI32(bytes) + 30
    Layout.LayoutOverflow {} => 0
  }
}

Import as Layout with import silk.layout.

Public declarations: 6.

Layout

pub struct Layout

A byte size paired with a non-zero power-of-two alignment.

Field bytes

pub bytes: usize

The number of addressable bytes required by the described storage.

Field alignment

pub alignment: usize

The required non-zero power-of-two byte alignment.

InvalidAlignment

pub struct InvalidAlignment

Reports the rejected alignment supplied to make.

Field alignment

pub alignment: usize

The zero or non-power-of-two alignment that was rejected.

LayoutOverflow

pub struct LayoutOverflow

Reports that repeat could not represent the aggregate byte size as usize.

of

pub fn of<T>() -> Layout

Returns the byte size and alignment required to store one value of T.

make

pub fn make(size: usize, alignment: usize) -> silk/layout.InvalidAlignment | silk/layout.Layout

Creates a layout from an explicit byte size and alignment.

Gotchas

If alignment is zero or is not a power of two, returns InvalidAlignment with that value.

repeat

pub fn repeat(layout: Layout, count: usize) -> silk/layout.Layout | silk/layout.LayoutOverflow

Returns a layout for count contiguous instances without wrapping the total byte size.

Details

The result keeps the input alignment and multiplies its byte size by count.

Gotchas

If the total byte size does not fit in usize, returns LayoutOverflow.