IntoIterator
The Iterator
trait tells you how to iterate once you have created an
iterator. The related trait
IntoIterator
defines how to create an iterator for a type. It is used automatically by the
for
loop.
Speaker Notes
This slide should take about 5 minutes.
IntoIterator
is the trait that makes for loops work. It is implemented by collection types such asVec<T>
and references to them such as&Vec<T>
and&[T]
. Ranges also implement it. This is why you can iterate over a vector withfor i in some_vec { .. }
butsome_vec.next()
doesn’t exist.
Click through to the docs for IntoIterator
. Every implementation of
IntoIterator
must declare two types:
Item
: the type to iterate over, such asi8
,IntoIter
: theIterator
type returned by theinto_iter
method.
Note that IntoIter
and Item
are linked: the iterator must have the same
Item
type, which means that it returns Option<Item>
The example iterates over all combinations of x and y coordinates.
Try iterating over the grid twice in main
. Why does this fail? Note that
IntoIterator::into_iter
takes ownership of self
.
Fix this issue by implementing IntoIterator
for &Grid
and creating a
GridRefIter
that iterates by reference. A version with both GridIter
and
GridRefIter
is available in this playground.
The same problem can occur for standard library types: for e in some_vector
will take ownership of some_vector
and iterate over owned elements from that
vector. Use for e in &some_vector
instead, to iterate over references to
elements of some_vector
.