diff --git a/docs/docs/noir/concepts/generics.md b/docs/docs/noir/concepts/generics.md index 0c1c27a2221..3e416eee093 100644 --- a/docs/docs/noir/concepts/generics.md +++ b/docs/docs/noir/concepts/generics.md @@ -104,3 +104,60 @@ impl Eq for MyStruct { ``` You can find more details on traits and trait implementations on the [traits page](../concepts/traits.md). + +## Manually Specifying Generics with the Turbofish Operator + +There are times when the compiler cannot reasonably infer what type should be used for a generic, or when the developer themselves may want to manually distinguish generic type parameters. This is where the `::<>` turbofish operator comes into play. + +The `::<>` operator can follow a variable or path and can be used to manually specify generic arguments within the angle brackets. +The name "turbofish" comes from that `::<>` looks like a little fish. + +Examples: +```rust +fn main() { + let mut slice = []; + slice = slice.push_back(1); + slice = slice.push_back(2); + // Without turbofish a type annotation would be needed on the left hand side + let array = slice.as_array::<2>(); +} +``` +```rust +fn double() -> u32 { + N * 2 +} +fn example() { + assert(double::<9>() == 18); + assert(double::<7 + 8>() == 30); +} +``` +```rust +trait MyTrait { + fn ten() -> Self; +} + +impl MyTrait for Field { + fn ten() -> Self { 10 } +} + +struct Foo { + inner: T +} + +impl Foo { + fn generic_method(_self: Self) -> U where U: MyTrait { + U::ten() + } +} + +fn example() { + let foo: Foo = Foo { inner: 1 }; + // Using a type other than `Field` here (e.g. u32) would fail as + // there is no matching impl for `u32: MyTrait`. + // + // Substituting the `10` on the left hand side of this assert + // with `10 as u32` would also fail with a type mismatch as we + // are expecting a `Field` from the right hand side. + assert(10 as u32 == foo.generic_method::()); +} +```