Silex Standard Library (Built-in Functions)

This document describes the built-in functions available in Silex. These functions are automatically available in your Silex code and can be invoked on the appropriate types (Arrays, Strings, Maps, etc.) or as static functions (e.g., Block::current()).

Please note:

• Gas Cost: Each function consumes a certain amount of gas when invoked. The gas cost is indicated below next to each function. But some functions can apply an additional dynamic gas.
• Optional Return: Some functions can return a value or null when the value is absent.
• Type Parameters: Some functions use a type variable T(0), T(1) (like in arrays or maps) simply meaning “whatever element type” your array or map uses.

Global Utility Functions

println

Signature:

println(value: Any)

Gas Cost: 1
Description: Prints a string representation of value (only effective if in debug mode).

debug

Signature:

debug(value: Any)

Gas Cost: 1
Description: Prints a debug-style (developer-friendly) representation of value (only effective if in debug mode).

panic

Signature:

panic(value: Any) -> Any

Return: whatever type you need (but code will never return)
Gas Cost: 1
Description: Aborts execution with the provided value as a message. It never returns normally.

assert

Signature:

assert(condition: bool)

Gas Cost: 1
Description: If condition is false, execution aborts with an assertion error.

require

Signature:

require(condition: bool, msg: string)

Gas Cost: 1
Description: If condition is false, execution aborts with the provided message, msg.

is_same_ptr

Signature:

is_same_ptr(value1: Any, value2: Any) -> bool

Gas Cost: 5
Description: Checks if value1 and value2 refer to the exact same internal reference.

Array Functions

Let arr be of type T[].

len

Signature:

arr.len() -> u32

Return: u32
Gas Cost: 1
Description: Returns the number of elements in arr.

push

Signature:

arr.push(value: T)

Gas Cost: 2
Description: Appends value to the end of arr.

remove

Signature:

arr.remove(index: u32) -> T

Gas Cost: 5
Description: Removes and returns the element at index, shifting subsequent elements to the left.
Throws an “OutOfBounds” error if index is invalid.

pop

Signature:

arr.pop() -> optional<T>

Gas Cost: 1
Description: Removes and returns the last element if it exists, or null if arr is empty.

slice

Signature:

arr.slice(range: range<u32>) -> T[]

Gas Cost: 5
Description: Returns a new array containing the elements in the given half-open range [start, end).
Throws an “InvalidRange” error if out of bounds or invalid.

contains

Signature:

arr.contains(value: T) -> bool

Gas Cost: 10
Description: Returns true if value is in arr.

get

Signature:

arr.get(index: u32) -> optional<T>

Gas Cost: 1
Description: Returns the element at index, or null if out of bounds.

first

Signature:

arr.first() -> optional<T>

Gas Cost: 1
Description: Returns the first element of arr, or null if empty.

last

Signature:

arr.last() -> optional<T>

Gas Cost: 1
Description: Returns the last element of arr, or null if empty.

Optional (T or null) Functions

These functions are invoked on a value that might be T or null.

is_none

Signature:

value.is_none() -> bool

Gas Cost: 1
Description: Returns true if value is null.

is_some

Signature:

value.is_some() -> bool

Gas Cost: 1
Description: Returns true if value is not null.

unwrap

Signature:

value.unwrap() -> T

Gas Cost: 1
Description: Returns the underlying value if not null. Throws an error otherwise.

unwrap_or

Signature:

value.unwrap_or(default_value: T) -> T

Gas Cost: 1
Description: Returns the underlying value if not null, or returns default_value if null.

expect

Signature:

value.expect(msg: string) -> T

Gas Cost: 15
Description: Returns the underlying value if not null. If null, the execution panics with the provided message, msg.

Map Functions

Let map be of type Map<K, V>.

len

Signature:

map.len() -> u32

Gas Cost: 1
Description: Returns the number of key-value pairs in map.

contains_key

Signature:

map.contains_key(key: K) -> bool

Gas Cost: 15
Description: Returns true if map contains key.

get

Signature:

map.get(key: K) -> optional<V>

Gas Cost: 15
Description: Returns the value for key or null if the key is not present.

insert

Signature:

map.insert(key: K, value: V) -> optional<V>

Gas Cost: 30
Description: Inserts or updates the key-value pair. Returns the old value if key was present, otherwise null.

remove

Signature:

map.remove(key: K) -> optional<V>

Gas Cost: 15
Description: Removes the key-value pair and returns the old value, or null if the key was not present.

clear

Signature:

map.clear()

Gas Cost: 5
Description: Removes all key-value pairs.

keys

Signature:

map.keys() -> [K]

Gas Cost: 20
Description: Returns an array of all keys.

values

Signature:

map.values() -> [V]

Gas Cost: 20
Description: Returns an array of all values.

string Functions

All are invoked on a string variable, e.g. my_string.len().

len

Signature:

str.len() -> u32

Gas Cost: 1
Description: Returns the length of the string in bytes (UTF-8 length).

trim

Signature:

str.trim() -> string

Gas Cost: 1
Description: Returns a new string with leading and trailing whitespace removed.

contains

Signature:

str.contains(value: string) -> bool

Gas Cost: 1
Description: Checks if value is a substring of str.

contains_ignore_case

Signature:

str.contains_ignore_case(value: string) -> bool

Gas Cost: 1
Description: Case-insensitive version of contains.

to_uppercase

Signature:

str.to_uppercase() -> string

Gas Cost: 1
Description: Returns str converted to uppercase.

to_lowercase

Signature:

str.to_lowercase() -> string

Gas Cost: 1
Description: Returns str converted to lowercase.

to_bytes

Signature:

str.to_bytes() -> u8[]

Gas Cost: 5
Description: Converts str into an array of its UTF-8 bytes.

index_of

Signature:

str.index_of(value: string) -> optional<u32>

Gas Cost: 3
Description: Finds the first index where value occurs. If not found, returns null.

last_index_of

Signature:

str.last_index_of(value: string) -> optional<u32>

Gas Cost: 3
Description: Finds the last index where value occurs. If not found, returns null.

replace

Signature:

str.replace(from: string, to: string) -> string

Gas Cost: 5
Description: Returns a copy of str with all occurrences of from replaced by to.

starts_with

Signature:

str.starts_with(value: string) -> bool

Gas Cost: 3
Description: Returns true if str begins with value.

ends_with

Signature:

str.ends_with(value: string) -> bool

Gas Cost: 3
Description: Returns true if str ends with value.

split

Signature:

str.split(at: string) -> [string]

Gas Cost: 5
Description: Splits str by the separator at and returns an array of substrings.

char_at

Signature:

str.char_at(index: u32) -> optional<string>

Gas Cost: 1
Description: Returns the character (as a 1-char string) at position index, or null if out of range.

is_empty

Signature:

str.is_empty() -> bool

Gas Cost: 1
Description: Returns true if str is empty.

matches

Signature:

str.matches(pattern: string) -> [string]

Gas Cost: 50
Description: Returns all non-overlapping matches of pattern within str as an array of strings.

substring (1 param)

Signature:

str.substring(start: u32) -> optional<string>

Gas Cost: 3
Description: Returns the substring from start index to the end, or null if out of range.

substring (2 params)

Signature:

str.substring(start: u32, end: u32) -> optional<string>

Gas Cost: 3
Description: Returns the substring from start (inclusive) up to end (exclusive), or null if out of range.

Range Functions

Silex supports a range type range<T> (e.g. range<u32>). These functions are methods on such range variables.

contains

Signature:

range.contains(value: T) -> bool

Gas Cost: 5
Description: Checks if value is within [start, end).

collect

Signature:

range.collect() -> T[]

Gas Cost: 20 (plus additional usage proportional to the size of the range)
Description: Creates an array of all values in [start, end).

max

Signature:

range.max() -> T

Gas Cost: 1
Description: Returns the end value of the range.

min

Signature:

range.min() -> T

Gas Cost: 1
Description: Returns the start value of the range.

count

Signature:

range.count() -> T

Gas Cost: 5
Description: Returns the number of elements in [start, end) as a T.

Integer Functions & Constants

Checked Arithmetic

For each unsigned integer type (u8, u16, u32, u64, u128, u256), the following methods exist:

• checked_add(other: T) -> optional<T>
• checked_sub(other: T) -> optional<T>
• checked_mul(other: T) -> optional<T>
• checked_div(other: T) -> optional<T>
• checked_rem(other: T) -> optional<T>

Gas Cost: 2 (for each operation) Description: Performs the specified arithmetic operation. If an overflow occurs, returns null; otherwise returns the resulting value.

MIN, MAX constants

For each of the unsigned integer types, the built-in constants MIN and MAX are available. You can reference them as u8::MIN, u8::MAX, u16::MIN, etc. Example:

let min_u32 = u32::MIN; // 0
let max_u32 = u32::MAX; // 4294967295

to_be_bytes / to_le_bytes

For each of u16, u32, u64, u128, u256, you have:

• value.to_be_bytes() -> u8[]
• value.to_le_bytes() -> u8[]

Gas Cost: 15
Description: Converts the integer into a big-endian or little-endian byte array. Typically, this returns the array (non-null).

Transaction Functions

Use these via the Transaction opaque type:

Transaction::current()

Signature:

Transaction::current() -> Transaction

Gas Cost: 5
Description: Returns the current transaction object in which the smart contract is running.

Once you have a Transaction (e.g. let tx: Transaction = Transaction::current();), you can call:

nonce

tx.nonce() -> u64

Gas Cost: 5
Description: Returns the nonce field of the current transaction.

hash

tx.hash() -> Hash

Gas Cost: 5
Description: Returns the cryptographic hash of the transaction.

source

tx.source() -> Address

Gas Cost: 5
Description: Returns the Address that originated the transaction.

fee

tx.fee() -> u64

Gas Cost: 5
Description: Returns the transaction’s fee.

signature

tx.signature() -> Signature

Gas Cost: 5
Description: Returns the signature object of the transaction.

Block Functions

Use these via the Block opaque type:

Block::current()

Block::current() -> Block

Gas Cost: 5
Description: Returns the current block object in which the contract is executing.

After obtaining a Block (e.g., let blk = Block::current();), you can call:

nonce

blk.nonce() -> u64

Gas Cost: 5
Description: Returns the block’s nonce.

timestamp

blk.timestamp() -> u64

Gas Cost: 5
Description: Returns the block’s timestamp.

height

blk.height() -> u64

Gas Cost: 5
Description: Returns the chain height at this block.

extra_nonce

blk.extra_nonce() -> u8[]

Gas Cost: 5
Description: Returns the block’s extra nonce field as a byte array.

hash

blk.hash() -> Hash

Gas Cost: 5
Description: Returns this block’s hash.

miner

blk.miner() -> Address

Gas Cost: 5
Description: Returns the miner’s address for the block.

version

blk.version() -> u8

Gas Cost: 5
Description: Returns the version number of the block.

tips

blk.tips() -> Hash[]

Gas Cost: 5
Description: Returns an array of hash references this block depends on (the block tips).

transactions_hashes

blk.transactions_hashes() -> Hash[]

Gas Cost: 50
Description: Returns an array of all transaction hashes included in this block.

transactions

blk.transactions() -> Transaction[]

Gas Cost: 250
Description: Returns an array of all Transaction objects in this block.

transactions_count

blk.transactions_count() -> u32

Gas Cost: 1
Description: Returns how many transactions are in this block.

Storage Functions

Storage::new()

Storage::new() -> Storage

Gas Cost: 5
Description: Creates a Storage object referring to this contract’s persistent storage. Typically you just use this once.

When you have a Storage, you can call:

load

storage.load(key: Any) -> optional<Any>

Gas Cost: 50
Description: Loads the stored value for key. Returns the value or null if not found.

has

storage.has(key: Any) -> bool

Gas Cost: 25
Description: Returns true if a value for key exists.

store

storage.store(key: Any, value: Any) -> optional<Any>

Gas Cost: 50
Description: Stores value for key, returning the old value if it existed, otherwise null.

delete

storage.delete(key: Any) -> optional<Any>

Gas Cost: 50
Description: Removes the key from storage, returning the old value if present, or null.

ReadOnlyStorage Functions

ReadOnlyStorage::new(contract_hash)

ReadOnlyStorage::new(contract: Hash) -> optional<ReadOnlyStorage>

Gas Cost: 15
Description: Returns a read-only view of another contract’s storage if it exists, otherwise null.

When you have a ReadOnlyStorage, you can call:

load

readonly_storage.load(key: Any) -> optional<Any>

Gas Cost: 50
Description: Reads the value for key in that contract’s storage, or null if not found.

has

readonly_storage.has(key: Any) -> bool

Gas Cost: 25
Description: Returns true if a value for key exists in the read-only storage.

MemoryStorage Functions

MemoryStorage::new()

MemoryStorage::new() -> MemoryStorage

Gas Cost: 5
Description: Creates a temporary in-memory storage (non-persistent).

For a MemoryStorage, you can call:

load

mem.load(key: Any) -> optional<Any>

Gas Cost: 50
Description: Loads a value for key from an in-memory map. Returns the value or null if not present.

has

mem.has(key: Any) -> bool

Gas Cost: 25
Description: Returns true if key is in the in-memory storage.

store

mem.store(key: Any, value: Any) -> optional<Any>

Gas Cost: 50
Description: Stores value, returning the old value if it existed, otherwise null.

delete

mem.delete(key: Any) -> optional<Any>

Gas Cost: 50
Description: Removes key, returning the old value if present, or null.

Address Functions

is_mainnet

addr.is_mainnet() -> bool

Gas Cost: 5
Description: Returns true if addr is a mainnet address.

is_normal

addr.is_normal() -> bool

Gas Cost: 5
Description: Returns true if addr is a “normal” address (not integrated, subaddress, etc.).

to_public_key_bytes

addr.to_public_key_bytes() -> Bytes

Gas Cost: 10
Description: Extracts the public key (32 bytes) as a Bytes object.

Address::from_string

Address::from_string(address_str: string) -> Address

Gas Cost: 75
Description: Constructs an Address from the given string representation. (If invalid, behavior may error or produce an invalid address.)

Hash Functions

to_bytes

hash_value.to_bytes() -> Bytes

Gas Cost: 5
Description: Converts the Hash to a 32-byte Bytes.

to_array

hash_value.to_array() -> u8[]

Gas Cost: 5
Description: Converts the Hash to an array of 32 u8.

to_u256

hash_value.to_u256() -> u256

Gas Cost: 5
Description: Interprets the Hash as a u256.

to_hex

hash_value.to_hex() -> string

Gas Cost: 20
Description: Returns a hex-encoded string of the hash (64 hex chars).

Hash::from_bytes

Hash::from_bytes(bytes: Bytes) -> Hash

Gas Cost: 75
Description: Constructs a Hash from a 32-byte Bytes.

Hash::from_array

Hash::from_array(bytes: u8[]) -> Hash

Gas Cost: 75
Description: Constructs a Hash from an array of 32 u8. Typically errors if the length is not 32.

Hash::from_u256

Hash::from_u256(value: u256) -> Hash

Gas Cost: 75
Description: Constructs a 32-byte Hash from a u256.

Hash::from_hex

Hash::from_hex(hex: string) -> Hash

Gas Cost: 75
Description: Parses a 64-char hex string into a 32-byte hash.

Hash::blake3

Hash::blake3(input: u8[]) -> Hash

Gas Cost: 3000
Description: Computes the BLAKE3 hash of input.

Hash::sha256

Hash::sha256(input: u8[]) -> Hash

Gas Cost: 7500
Description: Computes the SHA-256 hash of input.

Hash::zero

Hash::zero() -> Hash

Gas Cost: 1
Description: Returns the zeroed 32-byte hash.

Hash::max

Hash::max() -> Hash

Gas Cost: 1
Description: Returns a hash of all 0xFF bytes (the “maximum” possible hash).

Random Functions

Random::new()

Random::new() -> Random

Gas Cost: 5
Description: Creates a deterministic random generator object (seeded by the execution context).

The following methods can be called on a Random object:

next_u8 / next_u16 / next_u32 / next_u64 / next_u128 / next_u256

rng.next_u8()-> u8
rng.next_u16() -> u16
rng.next_u32() -> u32
rng.next_u64() -> u64
rng.next_u128()-> u128
rng.next_u256()-> u256

Gas Cost: 5 each
Description: Generates the next random number of the given width.

next_bool

rng.next_bool() -> bool

Gas Cost: 5
Description: Generates a random boolean.

Signature Functions

verify

Signature:

sig.verify(data: u8[], address: Address) -> bool

Gas Cost: 500
Description: Verifies that the signature sig is valid for the byte array data signed by address. Returns true if valid, false if invalid.

Signature::from_bytes

Signature::from_bytes(bytes: u8[]) -> Signature

Gas Cost: 75
Description: Creates a Signature from a byte array (usually 64 bytes).

Asset Functions

Asset::get_by_id

Asset::get_by_id(id: u64) -> optional<Asset>

Gas Cost: 1000
Description: Looks up the asset by a numeric ID. Returns the asset or null if not found.

Asset::create

Asset::create(
    id: u64,
    name: string,
    ticker: string,
    decimals: u8,
    max_supply: optional<u64>
) -> optional<Asset>

Gas Cost: 2500, with an additional 1 XEL of burned gas
Description: Creates a new asset with the given parameters. max_supply can be null if unlimited. Returns the newly created asset or null if creation fails.

Asset::get_by_hash

Asset::get_by_hash(hash: Hash) -> optional<Asset>

Gas Cost: 500
Description: Looks up the asset by its Hash. Returns the asset or null if not found.

Once you have an Asset, you can call:

get_max_supply

asset.get_max_supply() -> optional<u64>

Gas Cost: 5
Description: Returns the maximum supply if any, otherwise null.

get_supply

asset.get_supply() -> u64

Gas Cost: 15
Description: Returns the current supply of the asset.

get_name

asset.get_name() -> string

Gas Cost: 5
Description: Returns the asset’s full name (human-readable).

get_ticker

asset.get_ticker() -> string

Gas Cost: 5
Description: Returns the short ticker symbol.

get_hash

asset.get_hash() -> Hash

Gas Cost: 5
Description: Returns the unique Hash representing this asset.

mint

asset.mint(amount: u64) -> bool

Gas Cost: 500
Description: Increases the asset’s supply by amount, if allowed. Returns true if successful, false otherwise.

is_read_only

asset.is_read_only() -> bool

Gas Cost: 5
Description: Returns true if the asset cannot be modified (e.g. a read-only context).

get_contract_hash

asset.get_contract_hash() -> Hash

Gas Cost: 5
Description: If the asset is contract-scoped, returns the owning contract hash. Otherwise null.

get_id

asset.get_id() -> optional<u64>

Gas Cost: 5
Description: If the asset is numeric-based, returns its numeric ID, otherwise null.

transfer_ownership

asset.transfer_ownership(contract: Hash) -> bool

Gas Cost: 250
Description: If the asset is owned by the current contract, transfers ownership to the contract hash passed in parameter. Returns true if successful.

Misc. Built-ins

get_contract_hash()

get_contract_hash() -> Hash

Gas Cost: 5
Description: Returns the hash of the contract that is currently executing.

get_deposit_for_asset()

get_deposit_for_asset(asset: Hash) -> optional<u64>

Gas Cost: 5
Description: Returns how much of asset was deposited with the current contract call, or null if none.

get_balance_for_asset()

get_balance_for_asset(asset: Hash) -> u64

Gas Cost: 25
Description: Returns the contract’s current balance of asset.

transfer()

transfer(destination: Address, amount: u64, asset: Hash) -> bool

Gas Cost: 500
Description: Moves amount of asset out of the contract to destination. Returns true if successful, false otherwise.

burn()

burn(amount: u64, asset: Hash) -> bool

Gas Cost: 500
Description: Permanently removes amount of asset from the contract’s balance. Returns true if successful.

fire_event()

fire_event(id: u64, data: Any)

Gas Cost: 250 + an additional cost proportional to the size of data
Description: Fires an event with the given id and data. Events can be tracked externally.