Types¶
Vyper is a statically typed language, which means that the type of each variable (state and local) needs to be specified or at least known at compile-time. Vyper provides several elementary types which can be combined to form complex types.
In addition, types can interact with each other in expressions containing operators.
Value Types¶
The following types are also called value types because variables of these types will always be passed by value, i.e. they are always copied when they are used as function arguments or in assignments.
Boolean¶
Keyword: bool
A boolean is a type to store a logical/truth value.
Values¶
The only possible values are the constants True
and False
.
Operators¶
Operator | Description |
---|---|
x not y |
Logical negation |
x and y |
Logical conjunction |
x or y |
Logical disjunction |
x == y |
Equality |
x != y |
Inequality |
The operators or
and and
do not apply short-circuiting rules, i.e. both
x and y will always be evaluated.
Signed Integer (128 bit)¶
Keyword: int128
A signed integer (128 bit) is a type to store positive and negative integers.
Values¶
Signed integer values between -2127 and (2127 - 1), inclusive.
Operators¶
Comparisons¶
Comparisons return a boolean value.
Operator | Description |
---|---|
x < y |
Less than |
x <= y |
Less than or equal to |
x == y |
Equals |
x != y |
Does not equal |
x >= y |
Greater than or equal to |
x > y |
Greater than |
x
and y
must be of the type int128
.
Arithmetic Operators¶
Operator | Description |
---|---|
x + y |
Addition |
x - y |
Subtraction |
-x |
Unary minus/Negation |
x * y |
Multiplication |
x / y |
Division |
x**y |
Exponentiation |
x % y |
Modulo |
min(x, y) |
Minimum |
max(x, y) |
Maximum |
x
and y
must be of the type int128
.
Unsigned Integer (256 bit)¶
Keyword: uint256
An unsigned integer (256 bit) is a type to store non-negative integers.
Values¶
Integer values between 0 and (2256-1).
Note
Integer literals are interpreted as int128
by default. In cases where uint256
is more appropriate, such as assignment, the literal might be interpreted as uint256
. Example: _variable: uint256 = _literal
. In order to explicitly cast a literal to a uint256
use convert(_literal, uint256)
.
Operators¶
Comparisons¶
Comparisons return a boolean value.
Operator | Description |
---|---|
x < y |
Less than |
x <= y |
Less than or equal to |
x == y |
Equals |
x != y |
Does not equal |
x >= y |
Greater than or equal to |
x > y |
Greater than |
x
and y
must be of the type uint256
.
Arithmetic Operators¶
Operator | Description |
---|---|
x + y |
Addition |
x - y |
Subtraction |
uint256_addmod(x, y, z) |
Addition modulo z |
x * y |
Multiplication |
uint256_mulmod(x, y, z) |
Multiplication modulo z |
x / y |
Division |
x**y |
Exponentiation |
x % y |
Modulo |
min(x, y) |
Minimum |
max(x, y) |
Maximum |
x
, y
and z
must be of the type uint256
.
Bitwise Operators¶
Operator | Description |
---|---|
bitwise_and(x, y) |
AND |
bitwise_not(x, y) |
NOT |
bitwise_or(x, y) |
OR |
bitwise_xor(x, y) |
XOR |
shift(x, _shift) |
Bitwise Shift |
x
and y
must be of the type uint256
. _shift
must be of the type int128
.
Note
Positive _shift
equals a left shift; negative _shift
equals a right shift.
Values shifted above/below the most/least significant bit get discarded.
Decimals¶
Keyword: decimal
A decimal is a type to store a decimal fixed point value.
Values¶
A value with a precision of 10 decimal places between -2127 and (2127 - 1).
Operators¶
Comparisons¶
Comparisons return a boolean value.
Operator | Description |
---|---|
x < y |
Less than |
x <= y |
Less or equal |
x == y |
Equals |
x != y |
Does not equal |
x >= y |
Greater or equal |
x > y |
Greater than |
x
and y
must be of the type decimal
.
Arithmetic Operators¶
Operator | Description |
---|---|
x + y |
Addition |
x - y |
Subtraction |
-x |
Unary minus/Negation |
x * y |
Multiplication |
x / y |
Division |
x % y |
Modulo |
min(x, y) |
Minimum |
max(x, y) |
Maximum |
floor(x) |
Largest integer <= x . Returns int128 . |
ceil(x) |
Smallest integer >= x . Returns int128 . |
x
and y
must be of the type decimal
.
Address¶
Keyword: address
The address type holds an Ethereum address.
Values¶
An address type can hold an Ethereum address which equates to 20 bytes or 160 bits. It returns in hexadecimal notation with a leading 0x
.
Members¶
Member | Description |
---|---|
balance |
Query the balance of an address. Returns wei_value . |
codesize |
Query the code size of an address. Returns int128 . |
is_contract |
Query whether it is a contract address. Returns bool . |
Syntax as follows: _address.<member>
, where _address
is of the type address
and <member>
is one of the above keywords.
Unit Types¶
Vyper allows the definition of types with discrete units e.g. meters, seconds, wei, … . These types may only be based on either uint256
, int128
or decimal
.
Vyper has 3 unit types built in, which are the following:
Time¶
Keyword | Unit | Base type | Description |
---|---|---|---|
timestamp |
1 sec | uint256 |
This represents a point in time. |
timedelta |
1 sec | uint256 |
This is a number of seconds. |
Note
Two timedelta
can be added together, as can a timedelta
and a timestamp
, but not two timestamps
.
Custom Unit Types¶
Vyper allows you to add additional not-provided unit label to either uint256
, int128
or decimal
.
Custom units example:
# specify units used in the contract.
units: {
cm: "centimeter",
km: "kilometer"
}
Having defined the units they can be defined on variables as follows.
Custom units usage:
a: int128(cm)
b: uint256(km)
32-bit-wide Byte Array¶
Keyword: bytes32
This is a 32-bit-wide byte array that is otherwise similar to byte arrays.
Example:
# Declaration
hash: bytes32
# Assignment
self.hash = _hash
Operators¶
Keyword | Description |
---|---|
keccak256(x) |
Return the keccak256 hash as bytes32. |
concat(x, ...) |
Concatenate multiple inputs. |
slice(x, start=_start, len=_len) |
Return a slice of _len starting at _start . |
Where x
is a byte array and _start
as well as _len
are integer values.
Fixed-size Byte Arrays¶
Keyword: bytes
A byte array with a fixed size.
The syntax being bytes[maxLen]
, where maxLen
is an integer which denotes the maximum number of bytes.
On the ABI level the Fixed-size bytes array is annotated as bytes
.
Example:
example_bytes: bytes[100] = b"\x01\x02\x03"
Fixed-size Strings¶
Keyword: string
Fixed-size strings can hold strings with equal or fewer characters than the maximum length of the string.
On the ABI level the Fixed-size bytes array is annotated as string
.
Example:
example_str: string[100] = "Test String"
Operators¶
Keyword | Description |
---|---|
len(x) |
Return the length as an integer. |
keccak256(x) |
Return the keccak256 hash as bytes32. |
concat(x, ...) |
Concatenate multiple inputs. |
slice(x, start=_start, len=_len) |
Return a slice of _len starting at _start . |
Where x
is a byte array or string while _start
and _len
are integers.
The len
, keccak256
, concat
, slice
operators can be used with string
and bytes
types.
Reference Types¶
Reference types do not fit into 32 bytes. Because of this, copying their value is not as feasible as with value types. Therefore only the location, i.e. the reference, of the data is passed.
Fixed-size Lists¶
Fixed-size lists hold a finite number of elements which belong to a specified type.
Syntax¶
Lists can be declared with _name: _ValueType[_Integer]
. Multidimensional lists are also possible.
Example:
#Defining a list
exampleList: int128[3]
#Setting values
exampleList = [10, 11, 12]
exampleList[2] = 42
#Returning a value
return exampleList[0]
Structs¶
Structs are custom defined types that can group several variables.
Syntax¶
Structs can be accessed via struct.argname
.
Example:
#Defining a struct
struct MyStruct:
value1: int128
value2: decimal
exampleStruct: MyStruct
#Constructing a struct
exampleStruct = MyStruct({value1: 1, value2: 2})
#Accessing a value
exampleStruct.value1 = 1
Mappings¶
Mappings in Vyper can be seen as hash tables which are virtually initialized such that
every possible key exists and is mapped to a value whose byte-representation is
all zeros: a type’s default value. The similarity ends here, though: The key data is not actually stored
in a mapping, only its keccak256
hash used to look up the value. Because of this, mappings
do not have a length or a concept of a key or value being “set”.
It is possible to mark mappings public
and have Vyper create a getter.
The _KeyType
will become a required parameter for the getter and it will
return _ValueType
.
Note
Mappings are only allowed as state variables.
Syntax¶
Mapping types are declared as map(_KeyType, _ValueType)
.
Here _KeyType
can be any base or bytes type. Mappings, contract or structs are not support as key types.
_ValueType
can actually be any type, including mappings.
Example:
#Defining a mapping
exampleMapping: map(int128, decimal)
#Accessing a value
exampleMapping[0] = 10.1
Note
Mappings can only be accessed, not iterated over.
Built In Constants¶
Vyper has a few convenience constants builtin.
Type | Name | Value |
---|---|---|
address | ZERO_ADDRESS | 0x0000000000000000000000000000000000000000 |
bytes32 | EMPTY_BYTES32 | 0x0000000000000000000000000000000000000000000000000000000000000000 |
int128 | MAX_INT128 | 2**127 - 1 |
int128 | MIN_INT128 | -2**127 |
decimal | MAX_DECIMAL | (2**127 - 1) |
decimal | MIN_DECIMAL | (-2**127) |
uint256 | MAX_UINT256 | 2**256 - 1 |
Custom Constants¶
Custom constants can be defined at a global level in Vyper. To define a constant make use of the constant keyword.
Example:
TOTAL_SUPPLY: constant(uint256) = 10000000
total_supply: public(uint256)
@public
def __init__():
self.total_supply = TOTAL_SUPPLY
Advanced Example:
units: {
share: "Share unit"
}
MAX_SHARES: constant(uint256(share)) = 1000
SHARE_PRICE: constant(uint256(wei/share)) = 5
@public
def market_cap() -> uint256(wei):
return MAX_SHARES * SHARE_PRICE
Initial Values¶
In Vyper, there is no null
option like most programming languages have. Thus, every variable type has a default value. In order to check if a variable is empty, you will need to compare it to its type’s default value.
If you would like to reset a variable to its type’s default value, use the built-in clear()
function.
Here you can find a list of all types and default values:
Type | Default Value |
---|---|
bool |
False |
int128 |
0 |
uint256 |
0 |
decimal |
0.0 |
address |
0x0000000000000000000000000000000000000000 |
bytes32 |
'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00' |
Note
In bytes
the array starts with the bytes all set to '\x00'
Note
In reference types all the type’s members are set to their initial values.
Type Conversions¶
All type conversions in Vyper must be made explicitly using the built-in convert(a, b)
function. Currently, the following type conversions are supported:
Destination Type (b) | Input Type (a.type) | Allowed Inputs Values (a) | Additional Notes |
---|---|---|---|
bool |
bool |
— | Do not allow converting to/from the same type |
bool |
decimal |
MINNUM...MAXNUM |
Has the effective conversion logic of: return (a != 0.0) |
bool |
int128 |
MINNUM...MAXNUM |
Has the effective conversion logic of: return (a != 0) |
bool |
uint256 |
0...MAX_UINT256 |
Has the effective conversion logic of: return (a != 0) |
bool |
bytes32 |
(0x00 * 32)...(0xFF * 32) |
Has the effective conversion logic of: return (a != 0x00) |
bool |
bytes |
(0x00 * 1)...(0xFF * 32) |
Has the effective conversion logic of: return (a != 0x00) |
decimal |
bool |
True / False |
Result will be 0.0 or 1.0 |
decimal |
decimal |
— | Do not allow converting to/from the same type |
decimal |
int128 |
MINNUM...MAXNUM |
|
decimal |
uint256 |
0...MAXDECIMAL |
|
decimal |
bytes32 |
(0x00 * 32)...(0xFF * 32) |
|
decimal |
bytes |
(0x00 * 1)...(0xFF * 32) |
|
int128 |
bool |
True / False |
Result will be 0 or 1 |
int128 |
decimal |
MINNUM...MAXNUM |
Only allow input within int128 supported range, truncates the decimal value |
int128 |
int128 |
— | Do not allow converting to/from the same type |
int128 |
uint256 |
0...MAXNUM |
|
int128 |
bytes32 |
(0x00 * 32)...(0xFF * 32) |
|
int128 |
bytes |
(0x00 * 1)...(0xFF * 32) |
|
uint256 |
bool |
True / False |
Result will be 0 or 1 |
uint256 |
decimal |
0...MAXDECIMAL |
Truncates the decimal value |
uint256 |
int128 |
0...MAXNUM |
|
uint256 |
uint256 |
— | Do not allow converting to/from the same type |
uint256 |
bytes32 |
(0x00 * 32)...(0xFF * 32) |
|
uint256 |
bytes |
(0x00 * 1)...(0xFF * 32) |
|
bytes32 |
bool |
True / False |
Result will be either (0x00 * 32) or (0x00 * 31 + 0x01) |
bytes32 |
decimal |
MINDECIMAL...MAXDECIMAL |
Has the effective behavior of multiplying the decimal value by the decimal divisor 10000000000 and then converting that signed integer value to a bytes32 byte array |
bytes32 |
int128 |
MINNUM...MAXNUM |
|
bytes32 |
uint256 |
0...MAX_UINT256 |
|
bytes32 |
bytes32 |
— | Do not allow converting to/from the same type |
bytes32 |
bytes |
(0x00 * 1)...(0xFF * 32) |
Left-pad input bytes to size of 32 |