# WebAssembly types
Instead of using the
number type for all sorts of numeric values, AssemblyScript inherits WebAssembly's more specific integer and floating point types:
|AssemblyScript Type||WebAssembly type||Description|
| ||i32||A 32-bit signed integer.|
| ||i32||A 32-bit unsigned integer.|
| ||i64||A 64-bit signed integer.|
| ||i64||A 64-bit unsigned integer.|
| ||f32||A 32-bit float.|
| ||f64||A 64-bit float.|
| ||v128||A 128-bit vector 🦄.|
| ||anyref||An opaque host reference 🦄.|
|Small integer types|
| ||i32||An 8-bit signed integer.|
| ||i32||An 8-bit unsigned integer.|
| ||i32||A 16-bit signed integer.|
| ||i32||A 16-bit unsigned integer.|
| ||i32||A 1-bit unsigned integer.|
|Variable integer types|
| ||i32 or i64||A 32-bit signed integer in WASM32.|
A 64-bit signed integer in WASM64 🦄.
| ||i32 or i64||A 32-bit unsigned integer in WASM32.|
A 64-bit unsigned integer in WASM64 🦄.
| ||-||Indicates no return value.|
| ||?||Makes an educated guess. Internal only.|
# Type rules
AssemblyScript will complain when it sees an implicit conversion that might not actually be intended, quite similar to what a C compiler would do.
In AssemblyScript, the type assertions
expression as T known from TypeScript become explicit type conversions, essentially telling the compiler that the conversion is intended. In addition, each of the type names mentioned above, except aliases, also act as portable conversion built-ins that can be used just like
expression | 0.
Compared to TypeScript, type inference in AssemblyScript is limited because the type of each expression must be known in advance. This means that variable and parameter declarations must either have their type annotated or have an initializer. Without a type annotation and only an initializer, AssemblyScript will assume
i32 at first and only reconsider another type if the value doesn't fit (becomes
i64), is a float (becomes
f64) or irrefutably has another type than these, like the type of a variable, the return type of a function or a class type. Furthermore, functions must be annotated with a return type to help the compiler make the correct decisions, for example where a literal is returned or multiple return statements are present.
Basic types cannot be nullable, but class and function types can. Appending
| null declares a nullable type.
Assigning a value of one type to a target of another type can be performed without explicit casts where the full range of possible values can be represented in the target type, regardless of interpretation/signedness:
usize are aliases of either
u32 in WASM32 respectively
u64 in WASM64 🦄.
var i8val: i8 = -128 // 0x80 var u8val: u8 = i8val // becomes 128 (0x80) var i16val: i16 = i8val // becomes -128 through sign-extension (0xFF80) var u16val: u16 = i8val // becomes 65408 through masking (0xFF80) var f32val: f32 = i8val // becomes -128.0
Comparing two values of different types can be performed without an explicit cast under the same rules as outlined in assignability above
- if the comparison is absolute (
- if the comparison is relative (
<=) and both types have the same signedness
because WebAssembly has distinct operations for signed and unsigned comparisons. The comparison uses the larger type and returns
# Bit shifts
The result of a bit shift (
>>) is the left type, with the right type implicitly converted to the left type, performing an arithmetic shift if the left type is signed and a logical shift if the left type is unsigned.
The result of an unsigned right shift (
>>>) is the left type (signedness is retained), with the right type implicitly converted to the left type, but always performing a logical shift.
Note that only the
log2(sizeof<T>()) least signficant bits of the shift affect the result:
|i8 / u8||3|
|i16 / u16||4|
|i32 / u32||5|
|i64 / u64||6|
If the left type is a float, an error is emitted.
# Macro types
The following macro types provide access to related types that would otherwise be impossible to obtain.
| ||Obtains the underlying native type of |
| ||Obtains the index type of a collection based on the indexed access overload.|
| ||Obtains the value type of a collection based on the indexed access overload.|
| ||Obtains the return type of a function type.|