modern-move-syntax

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Overview

The Move 2024 edition introduced method syntax and several convenience features. AI agents frequently fall back to pre-2024 function-call patterns from training data. This skill covers every modern syntax pattern.

All patterns sourced from https://move-book.com/guides/code-quality-checklist

Method Syntax for Common Operations

Use method-call syntax (dot notation) instead of module function calls.

Coin and Balance

// WRONG — legacy function-call syntax
let value = coin::value(&payment);
let balance = coin::into_balance(payment);
balance::join(&mut pool.reserve, balance);
let coin = coin::from_balance(balance::split(&mut pool.reserve, amount), ctx);

// CORRECT — method syntax
let value = payment.value();
let balance = payment.into_balance();
pool.reserve.join(balance);
let coin = coin::from_balance(pool.reserve.split(amount), ctx);

// BEST — chained method calls
let balance = payment.split(amount, ctx).into_balance();

TxContext

// WRONG
tx_context::sender(ctx)

// CORRECT
ctx.sender()

UID and Object

// WRONG
object::delete(id);

// CORRECT
id.delete();

String Literals

Use quoted string literals directly, not std::string::utf8() or byte-string conversion.

// WRONG
use std::string;
let s = string::utf8(b"hello");

// ALSO WRONG — unnecessary conversion
let s = b"hello".to_string();

// CORRECT — direct string literals (2024 edition)
let s = "hello";                    // String (UTF-8)
let ascii = "hello";                // also works for ASCII strings
let s = b"hello".to_string();      // still valid but prefer quoted form
let ascii = b"hello".to_ascii_string(); // explicit ASCII when needed

Vector Literals and Methods

Use vector literal syntax and method calls instead of module functions.

// WRONG
let mut v = vector::empty();
vector::push_back(&mut v, 10);
let first = vector::borrow(&v, 0);
let len = vector::length(&v);

// CORRECT
let mut v = vector[10];
let first = &v[0];
let len = v.length();
v.push_back(20);

Collection Index Syntax

// WRONG
let val = vec_map::get(&map, &key);

// CORRECT
let val = &map[&key];

Option Macros

Use macros instead of manual is_some / destroy_some patterns.

// WRONG
if (opt.is_some()) {
    let value = opt.destroy_some();
    call_function(value);
};

// CORRECT
opt.do!(|value| call_function(value));

Default values

// WRONG
let value = if (opt.is_some()) { opt.destroy_some() } else { default };

// CORRECT
let value = opt.destroy_or!(default);

Loop Macros

// WRONG — manual counter loop
let mut i = 0;
while (i < 32) {
    do_action();
    i = i + 1;
};

// CORRECT — do! macro
32u8.do!(|_| do_action());

Range-based loops

// Iterate over a numeric range
let mut sum = 0;
10u64.do!(|i| { sum = sum + i });  // i goes 0..9

// With index for more complex logic
let mut results = vector[];
5u64.do!(|i| results.push_back(i * i));  // [0, 1, 4, 9, 16]

Vector iteration

// WRONG
let mut i = 0;
while (i < vec.length()) {
    call_function(&vec[i]);
    i = i + 1;
};

// CORRECT
vec.do_ref!(|e| call_function(e));

Vector creation from range

// WRONG
let mut v = vector[];
let mut i = 0;
while (i < 32) { v.push_back(i); i = i + 1; };

// CORRECT
let v = vector::tabulate!(32, |i| i);

Fold and filter

// fold
let sum = source.fold!(0, |acc, v| { acc + v });

// filter (requires T: drop)
let filtered = source.filter!(|e| e > 10);

Struct Unpacking: .. Syntax

Use .. to ignore unused fields when destructuring in 2024 edition.

// WRONG
let MyStruct { id, field_1: _, field_2: _, field_3: _ } = value;

// CORRECT
let MyStruct { id, .. } = value;

Renamed Standard Library Functions

Some standard library functions have been renamed. Using the old name produces a deprecation warning or compile error.

// WRONG — deprecated, renamed
dynamic_field::exists_(&id, key)

// CORRECT
dynamic_field::exists(&id, key)

Positional Fields (Tuple Structs)

Structs can use positional fields instead of named fields:

// Named fields (traditional)
public struct Wrapper has copy, drop, store { value: u64 }

// Positional fields (2024 edition)
public struct Wrapper(u64) has copy, drop, store;

// Access by position
let w = Wrapper(42);
let val = w.0;

Positional structs are useful for newtype wrappers and dynamic field keys (see naming-conventions skill).

Public Structs

The public keyword on structs controls visibility of the struct's fields. Without public, fields are module-private — only the defining module can construct or destructure the struct.

// Fields visible only within this module
struct Config has key { id: UID, admin: address }

// Fields visible to other modules
public struct Token has key, store { id: UID, value: u64 }

Use public when other modules need to read fields or construct/destructure the struct. Omit it for encapsulation.

Enums

Move 2024 supports enum types:

public enum Color {
    Red,
    Green,
    Blue,
    Custom(u8, u8, u8),
}

public fun is_red(c: &Color): bool {
    match (c) {
        Color::Red => true,
        _ => false,
    }
}

Enums can have variants with positional fields, named fields, or no fields. Use match expressions for exhaustive pattern matching. Enums cannot have the key ability — they cannot be objects directly, but they can be stored as fields inside objects.

Quick Reference