Invalid type passed!
Received:
{type}
Expected one of:
{asideVariants.join(", ")}
: <>
{title &&
{title}
}
{children}
}
;
};
Tolk supports type conversions: either automatic or explicit via the `as` operator.
## Automatic conversions
Assignable types can be provided explicitly:
```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 takeOptInt(v: int?) {}
fun main() {
takeOptInt(100); // ok, `int` to `int?`
takeOptInt(null); // ok, `null` to `int?`
}
```
Certain conversions are automatic:
* `int` to `intN`.
* `AliasForT` and `T` (bidirectional).
* `Cell` to `cell`.
```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 autocast() {
var number: int32 = 100; // auto cast `int` to `int32`
}
```
Non-assignable types cause a compilation error:
```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 main() {
var number: int = true;
}
/// file.tolk:2:23: error: can not assign `bool` to variable of type `int`
/// hint: use `as` operator for UNSAFE casting: ` as int`
///
/// // in function `main`
/// 2 | var number: int = true;
/// | ^^^^
```
## Smart casts
Once a variable is checked, the compiler narrows its type. For instance, if a variable [could be `null`](/languages/tolk/types/nullable) before the check, and the condition is confirmed to be true, the variable's type will not allow `null` in the true block anymore.
```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"]}}
if (lastCell != null) {
// here lastCell is `cell`, not `cell?`
}
```
## Operator `is` for union types
Given a [union type](/languages/tolk/types/unions) `T1 | T2 | ...`, the `is` operator performs a runtime type test, narrowing the 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 demo(v: int | Point | cell) {
if (v is Point) {
return v.x + v.y;
}
// v is `int | cell` here
}
```
## Non-null assertion with operator `!`
The `!` operator bypasses the compiler's nullability check. It is similar to `!` in TypeScript and `!!` in Kotlin.
```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 doSmth(c: cell) {}
fun analyzeStorage(nCells: int, lastCell: cell?) {
// Say, according to the logic of this program,
// having non-zero number of `nCells` must mean
// that the `lastCell` is not `null`
if (nCells) {
// Therefore, one can explicitly instruct
// the compiler to recognize that fact
doSmth(lastCell!);
}
}
```
## Unsafe cast with operator `as`
When non-trivial type transformations are required, the `as` operator overrides the restrictions by performing an unsafe type cast.
For instance, `bool` cannot be assigned directly to `int`. However, a direct cast using the `as` operator is valid since booleans are represented as [TVM](/tvm/overview) integers: `true` is -1, and `false` is 0.
```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 number: int = true as int; // -1
```
Not all transformations are possible. For example, `42 as cell` is invalid. When a cast is inappropriate, the compiler indicates this in diagnostic messages.
The `as` operator converts types that share the same TVM representation:
* `address` is a TVM slice, so `someAddr as slice` is valid.
* Conversely, `someSlice as address` is valid.
* `bitsN`, where `N` is between 1 and 1023, is a TVM slice, so `someSlice as bitsN` is valid.
* `intN`, where `N` is between 1 and 257, is a TVM integer, so `someInt64 as int32` is valid.
* `bool` is as TVM integer, so `someBool as int` and `someBool as int32` result in -1 or 0.
* Enums are TVM integers, so `someColor as int` is valid.
Finally, the `as` operator cannot be applied to unions: `v as Point` is incorrect. Use the `is` operator and smart casts.