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auto merge of #17836 : typelist/rust/guide-tuples, r=steveklabnik 

Currently, the Guide says tuples "are only equivalent if the arity, types, and values are all identical", before presenting an example that uses `==` to compare two tuples whose arity and contained types match. This is misleading, because it implies that `==` can dynamically check whether two tuples have the same arity and contained types, whereas trying to do this would lead to a compiler error.

I tried to avoid destroying the flow of this section, but I'm not sure if I've been successful.
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bors 2014-10-08 01:02:10 +00:00
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@ -914,12 +914,23 @@ or 'breaks up,' the tuple, and assigns the bits to three bindings.
This pattern is very powerful, and we'll see it repeated more later.
The last thing to say about tuples is that they are only equivalent if
the arity, types, and values are all identical.
There also a few things you can do with a tuple as a whole, without
destructuring. You can assign one tuple into another, if they have the same
arity and contained types.
```rust
let mut x = (1i, 2i);
let y = (2i, 3i);
x = y;
```
You can also check for equality with `==`. Again, this will only compile if the
tuples have the same type.
```rust
let x = (1i, 2i, 3i);
let y = (2i, 3i, 4i);
let y = (2i, 2i, 4i);
if x == y {
println!("yes");
@ -928,7 +939,7 @@ if x == y {
}
```
This will print `no`, as the values aren't equal.
This will print `no`, because some of the values aren't equal.
One other use of tuples is to return multiple values from a function: