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Type aliases: Restore personhood to people without a home #438

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Jul 14, 2020
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Type aliases: Restore personhood to people without a home #438

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14 changes: 7 additions & 7 deletions content/types/type-aliases.md
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Original file line number Diff line number Diff line change
Expand Up @@ -67,10 +67,10 @@ interface HasName
interface HasAge
fun age(): U32

interface HasAddress
fun address(): String
interface HasFeelings
fun feeling(): String

type Person is (HasName & HasAge & HasAddress)
type Person is (HasName & HasAge & HasFeelings)
```

This use of complex types applies to traits, not just interfaces:
Expand All @@ -82,13 +82,13 @@ trait HasName
trait HasAge
fun age(): U32 => 42

trait HasAddress
fun address(): String => "3 Abbey Road"
trait HasFeelings
fun feeling(): String => "Great!"

type Person is (HasName & HasAge & HasAddress)
type Person is (HasName & HasAge & HasFeelings)
```

There's another new concept here: the type has a `&` in it. This is similar to the `|` of a __union__ type: it means this is an __intersection__ type. That is, it's something that must be _all_ of `HasName`, `HasAge` _and_ `HasAddress`.
There's another new concept here: the type has a `&` in it. This is similar to the `|` of a __union__ type: it means this is an __intersection__ type. That is, it's something that must be _all_ of `HasName`, `HasAge` _and_ `HasFeelings`.

But the use of `type` here is exactly the same as the enumeration example above, it's just providing a name for a type that is otherwise a bit tedious to type out over and over.

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