Inner items do not inherit type or const parameters from the functions
they are embedded in.
Erroneous code example:
```compile_fail,E0401
fn foo<T>(x: T) {
fn bar(y: T) { // T is defined in the "outer" function
// ..
}
bar(x);
}
```
Nor will this:
```compile_fail,E0401
fn foo<T>(x: T) {
type MaybeT = Option<T>;
// ...
}
```
Or this:
```compile_fail,E0401
fn foo<T>(x: T) {
struct Foo {
x: T,
}
// ...
}
```
Items inside functions are basically just like top-level items, except
that they can only be used from the function they are in.
There are a couple of solutions for this.
If the item is a function, you may use a closure:
```
fn foo<T>(x: T) {
let bar = |y: T| { // explicit type annotation may not be necessary
// ..
};
bar(x);
}
```
For a generic item, you can copy over the parameters:
```
fn foo<T>(x: T) {
fn bar<T>(y: T) {
// ..
}
bar(x);
}
```
```
fn foo<T>(x: T) {
type MaybeT<T> = Option<T>;
}
```
Be sure to copy over any bounds as well:
```
fn foo<T: Copy>(x: T) {
fn bar<T: Copy>(y: T) {
// ..
}
bar(x);
}
```
```
fn foo<T: Copy>(x: T) {
struct Foo<T: Copy> {
x: T,
}
}
```
This may require additional type hints in the function body.
In case the item is a function inside an `impl`, defining a private helper
function might be easier:
```
# struct Foo<T>(T);
impl<T> Foo<T> {
pub fn foo(&self, x: T) {
self.bar(x);
}
fn bar(&self, y: T) {
// ..
}
}
```
For default impls in traits, the private helper solution won't work, however
closures or copying the parameters should still work.