CODEWITHSUNDEEP
rust
Hao Li
Hao Li

Reputation: 1762

How to make a generic struct as function parameter

I tried to write a function that takes a generic struct as a parameter:

struct S<T> {
    v: T,
}

fn foo(a: &S) {
    a.v
}

But an error occurs:

error[E0107]: wrong number of type arguments: expected 1, found 0
 --> src/main.rs:5:12
  |
5 | fn foo(a: &S) {
  |            ^ expected 1 type argument

error: aborting due to previous error

First update

After changing to

struct S<T> {
    v: T,
}

fn foo<T>(a: &S<T>) -> T {
    a.v
}

Another error occurs:

error[E0507]: cannot move out of `a.v` which is behind a shared reference
 --> src/main.rs:6:5
  |
6 |     a.v
  |     ^^^ move occurs because `a.v` has type `T`, which does not implement the `Copy` trait

error: aborting due to previous error

Second update

Finally, I got what I want:

struct S<T> {
    v: T,
}

fn foo<T: Copy>(a: &S<T>) -> T {
    a.v
}

Upvotes: 1

Views: 84

Answers (1)

edkeveked
edkeveked

Reputation: 18401

You missed the generic parameter

struct S<T> {
    v: T,
}

fn foo<T>(a: S<T>) -> T {
    a.v
}

Or use the Copy bound

fn foo<T: Copy>(a: &S<T>) -> T {
  a.v
}

Upvotes: 2

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