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ARC-43 No Length in Dynamic Arrays of Static Types #214

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ARC-43 No Length in Dynamic Arrays of Static Types #214

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No Length in Dynamic Arrays of Static Types
joe-p Jun 16, 2023
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joe-p Jun 16, 2023
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SudoWeezy Jun 16, 2023
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add clarity to spec
joe-p Jun 23, 2023
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joe-p Jun 23, 2023
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44 changes: 44 additions & 0 deletions ARCs/arc-0043.md
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---
arc: 43
title: No Length in Dynamic Arrays of Static Types
description: Remove the length prefix in dynamic arrays if the type is static
author: Joe Polny (@joe-p)
discussions-to: https://github.com/algorandfoundation/ARCs/issues/214
status: Draft
type: Standards Track
category: ARC
created: 2023-07-16
requires: 4
---
## Abstract
According to [ARC-0004](./arc-0004.md), all dynamic arrays must be prefixed with their element length encoded as a uint16. This information is not necessary when the element type is static and thus it should be removed for simplicity sake. The exception is if the array is encoded inside of a tuple or array.

## Motivation
ABI-compliant contracts freuquently work with `string` types but all of the AVM opcodes expect regular byteslices, wihch means extra opcodes are needed when using a `string` with opcodes, which is quite common.

## Specification
The key words "**MUST**", "**MUST NOT**", "**REQUIRED**", "**SHALL**", "**SHALL NOT**", "**SHOULD**", "**SHOULD NOT**", "**RECOMMENDED**", "**MAY**", and "**OPTIONAL**" in this document are to be interpreted as described in <a href="https://www.ietf.org/rfc/rfc2119.txt">RFC-2119</a>.

If encoding a dynamic array, `x`, of type `T[]`, and the element type `T` is static, the array is encoded by simply concatenating all values of `x` together. If the array is inside of a tuple or array, the number of elements in `x` must be encoded as `uint16` and prefixed to the array, as per [ARC-0004](./arc-0004.md).

## Rationale
This will reduce the amount of bytes required when encoding dynamic arrays and make it easier to work with `byte[]` and `string` types in the AVM.

## Backwards Compatibility
This change is not backwards compatible with [ARC-0004](./arc-0004.md).

## Test Cases
N/A

## Reference Implementation
`[1, 2, 3]` encoded as `uint8[]`

[ARC-0004](./arc-0004.md): `0x 0003 01 02 03`

This ARC: `0x 01 02 03`

## Security Considerations
None

## Copyright
Copyright and related rights waived via <a href="https://creativecommons.org/publicdomain/zero/1.0/">CCO</a>.