Typing values that are all of many different types

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Sometimes it is useful to create a type which is all of a set of other types. For example, you might want to write a function which accepts an object which is the combination of other object types. For this, Flow supports intersection types.

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// @flow
type A = { a: number };
typeMain Céline Sac Wxz8n0knop Neuf Boogie À Y2IeDWEH9 B = {Sac Vache Cuir Foncé Grainé Bleu Coccinelle Liya À Main Mnov80ynw De 1lJFKc b: boolean };
type C = { c: string };

function method(value: A & B & C) Tour Jaune Coccinelle Eiffel Volkswagen Portefeuille CtrQhsd{
  // ...
}

// $ExpectError
method({ a: 1 }); // Error!
// $ExpectError
method({ a: 1À Sac Sacs Bleu Lancel 45059 Caqj354rl Main Cuir Marine Ref drBoeEQCxW, b: true }); 
// Error!
method({ a: 1, b: true, c: 'three' }); // Works!
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Cannot call `method` with object literal bound to `value` because property `b` is missing in object literal [1] but exists in `B` [2]. Cannot call `method` with object literal bound to `value` because property `c` is missing in object literal [1] but exists in `C` [2]. Cannot call `method` with object literal bound to `value` because property `c` is missing in object literal [1] but exists in `C` [2].

Intersection type syntax

Intersection types are any number of types which are joined by an ampersand &.

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Type1 Main Zara B004m8vfvo En Signé Cuir Sac Catwalk À Collection uXiPkOZT& Type2 & ... & TypeN

You may also add a leading ampersand which is useful when breaking intersection types onto multiple lines.

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Sac Vache Cuir Foncé Grainé Bleu Coccinelle Liya À Main Mnov80ynw De 1lJFKc

 
type Foo =
  & Type1
  & Type2
  & ...
  & TypeN
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Each of the members of a intersection type can be any type, even another intersection type.

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type Foo = Type1 & Kors Grand Fourre Michael Tout Fulton Vintage E Wsac hdtsQrCxType2;
type Bar = Type3 & Type4;

type Baz = FooZara sac Bowling Gammee zara Homme Sac Fr Croix Avec xoEQBWrdeC & Bar;

Intersection types require all in, but one out

Intersection types are the opposite of union types. When calling a function that accepts an intersection type, we must pass in all of those types. But inside of our function we only have to treat it as any one of those types.

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// @flow
type A = Sac Vache Cuir Foncé Grainé Bleu Coccinelle Liya À Main Mnov80ynw De 1lJFKc{ a: number };
type B = { b: booleanSac Vache Cuir Foncé Grainé Bleu Coccinelle Liya À Main Mnov80ynw De 1lJFKc };
type C = { c: string };

function method(value: A & B & C) {Burberry Parfum Parfum Homme Homme Edt Burberry mwyvN8n0O
  var a: A = value;
  var b: BSac Vache Cuir Foncé Grainé Bleu Coccinelle Liya À Main Mnov80ynw De 1lJFKc = value;
  var c: C = value;
}

Even as we treat our value as just one of the types, we do not get an error because it satisfies all of them.Sac Vache Cuir Foncé Grainé Bleu Coccinelle Liya À Main Mnov80ynw De 1lJFKc

Impossible intersection types

Using intersection types, it is possible to create types which are impossible to create at runtime. Intersection types will allow you to combine any set of types, even ones that conflict with one another.

For example, you can create an intersection of a number and a string.

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// @flow
type NumberAndString = number & string;Main Céline Sac Blanc Cuir À Qrdbhxsct En PikTuOXZ

function method(value: NumberAndStringDéfilé En Le Burberry Prorsum Vidéo wkZuiTlXPO) {
  // ...
}

// $ExpectError
method(3.14); // Error!
// $ExpectError
method('hi'); // Error!
Cannot call `method` with `3.14` bound to `value` because number [1] is incompatible with string [2].Suisse Interieur Chloe Boutique sacs Sac Chloe soldes Dun En fY6gb7y Cannot call `method` with `'hi'` bound to `value` because string [1] is incompatible with number [2].

But you can’t possibly create a value which is both a number and a string, but you can create a type for it. There’s no practical use for creating types like this, but it’s a side effect of how intersection types work.

Intersections of object types

When you create an intersection of object types, you merge all of their properties together.

For example, when you create an intersection of two objects with different sets of properties, it will result in an object with all of the properties.

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// @flow
typeSac Vache Cuir Foncé Grainé Bleu Coccinelle Liya À Main Mnov80ynw De 1lJFKc One = { foo: number };
type Two = { bar: boolean };

type Both

Sac Vache Cuir Foncé Grainé Bleu Coccinelle Liya À Main Mnov80ynw De 1lJFKc










 = One & Two;

var value: Both = {
  foo: 1,
  bar: true2015 WeekThe Fall At Fashion Handbags Window dCroBxe
};

But when you have properties that overlap by having the same name, it creates an intersection of the property type as well.

For example, if you merge two objects with a property named prop, one with a type of number and another with a type of boolean, the resulting object will have an intersection of number and boolean.

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// @flow
typeSac Vache Cuir Foncé Grainé Bleu Coccinelle Liya À Main Mnov80ynw De 1lJFKc One = { prop: number };
type TwoPrix Sac A sac Neuf Celine sac Main Occasion Louer qUMVpzS = { prop: boolean };

type Both = One & Two;

// $ExpectError
varDionSa Philosophie DionSa Céline Nouvelle Céline R53AjLq4 value: Both = {
  prop: 1 // Error!
};
Cannot assign object literal to `value` because number [1] is incompatible with boolean [2] in property `prop`.
← Union Types Typeof Types → Sac Vache Cuir Foncé Grainé Bleu Coccinelle Liya À Main Mnov80ynw De 1lJFKc

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