Invalid type passed!
Received:
{type}
Expected one of:
{asideVariants.join(", ")}
: <>
{title &&
{title}
}
{children}
}
;
};
`unknown` represents any single-slot [TVM](/tvm/overview) value with contents unknown at compile-time.
## Primary use
`tuple` is an alias for `array`:
```tolk theme={"theme":{"light":"github-light-default","dark":"dark-plus"},"languages":{"custom":["/resources/grammars/tolk.tmLanguage.json","/resources/grammars/tlb.tmLanguage.json","/resources/grammars/fift.tmLanguage.json","/resources/grammars/tasm.tmLanguage.json","/resources/grammars/func.tmLanguage.json"]}}
// declared in stdlib
type tuple = array
```
Because of that, `tuple` has all the array methods: `push`, `size`, and others. Such arrays are opaque, so the `push` method accepts values of any type:
```tolk theme={"theme":{"light":"github-light-default","dark":"dark-plus"},"languages":{"custom":["/resources/grammars/tolk.tmLanguage.json","/resources/grammars/tlb.tmLanguage.json","/resources/grammars/fift.tmLanguage.json","/resources/grammars/tasm.tmLanguage.json","/resources/grammars/func.tmLanguage.json"]}}
var t = []; // array
t.push(1);
t.push(null);
t.push(Point { x: 10, y: 20 });
```
Read more about [arrays and tuples](/languages/tolk/types/tuples).
## Manual type casts with `as` operator
Any type `T` can be cast to `unknown` using the `as` operator. If `T` is a primitive that fits in a single stack slot, the cast is a no-op. Otherwise, the object is packed into a sub-tuple:
```tolk theme={"theme":{"light":"github-light-default","dark":"dark-plus"},"languages":{"custom":["/resources/grammars/tolk.tmLanguage.json","/resources/grammars/tlb.tmLanguage.json","/resources/grammars/fift.tmLanguage.json","/resources/grammars/tasm.tmLanguage.json","/resources/grammars/func.tmLanguage.json"]}}
var u = 5 as unknown;
// stack: 5
u as int;
// stack: 5
var u2 = (10, 20) as unknown;
// stack: [ 10 20 ] (a TVM tuple)
u2 as (int, int);
// stack: 10 20 (two integers)
```
To perform meaningful operations on an `unknown` value, [cast it to a known type with `as`](#be-extremely-careful-using-unknown).
## Exception arguments
In TVM, an exception can carry some value in an arbitrary stack slot. The syntax `throw (code, arg)` allows attaching an argument `arg` of `unknown` type:
```tolk theme={"theme":{"light":"github-light-default","dark":"dark-plus"},"languages":{"custom":["/resources/grammars/tolk.tmLanguage.json","/resources/grammars/tlb.tmLanguage.json","/resources/grammars/fift.tmLanguage.json","/resources/grammars/tasm.tmLanguage.json","/resources/grammars/func.tmLanguage.json"]}}
fun load(id: int) {
// ...
throw (NOT_FOUND, id)
}
fun demo() {
try {
load(456);
} catch (ex, arg) {
// `arg` is `unknown`
if (ex == NOT_FOUND) {
arg as int; // 456
}
}
}
```
Composite argument values are allowed. For example, the structure `Point` in `throw (code, Point { ... })` will be packed to a single slot of `unknown` type. Casting `arg as Point` will unpack that `unknown` back.
## Be extremely careful using `unknown`
Using `unknown` incorrectly may lead to runtime errors or stack corruption. Always extract a value of the exact type it was originally stored in.
For example, this usage is invalid:
```tolk theme={"theme":{"light":"github-light-default","dark":"dark-plus"},"languages":{"custom":["/resources/grammars/tolk.tmLanguage.json","/resources/grammars/tlb.tmLanguage.json","/resources/grammars/fift.tmLanguage.json","/resources/grammars/tasm.tmLanguage.json","/resources/grammars/func.tmLanguage.json"]}}
fun demoInvalid() {
var x: int | slice = 123;
var t = array [x];
t.get(0) as int | slice; // runtime error
}
```
There, a runtime error occurs because the `x` has been smart cast to `int` when it was placed into the array `t`:
```tolk theme={"theme":{"light":"github-light-default","dark":"dark-plus"},"languages":{"custom":["/resources/grammars/tolk.tmLanguage.json","/resources/grammars/tlb.tmLanguage.json","/resources/grammars/fift.tmLanguage.json","/resources/grammars/tasm.tmLanguage.json","/resources/grammars/func.tmLanguage.json"]}}
fun demoInvalid() {
var x: int | slice = 123;
// `x` is smart-cast to `int`
var t = array [x];
// As such, `t` is [123], containing an integer.
// Because of the unsafe type cast,
// `t.get(0)` is viewed as a tagged union `int|slice` and not an `int`,
// triggering a runtime error.
t.get(0) as int | slice;
}
```
## Stack layout and serialization
A value of type `unknown` takes a single TVM slot with any valid value at runtime. It cannot be serialized because the exact value type is not known.