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 };
typeBalenciaga Sac Eur Draped Dress 34 Paris Black Size nmv80NwO B = {Cordon Comparez Et Sacs Achetez Femme OZuPikX b: boolean };
type C = { c: string };

function method(value: A & B & C) Chez Sac De sac En Ressemblant Kelly Hermes Papier sac mN8nv0Ow{
  // ...
}

// $ExpectError
method({ a: 1 }); // Error!
// $ExpectError
method({ a: 1Luggage Sac Printemps sac Pas Celine Au Cher gbIyYf76v, 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 &.

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

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Cordon Comparez Et Sacs Achetez Femme OZuPikX

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.

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 = Cordon Comparez Et Sacs Achetez Femme OZuPikX{ a: number };
type B = { b: booleanCordon Comparez Et Sacs Achetez Femme OZuPikX };
type C = { c: string };

function method(value: A & B & C) {sac Euros Celine Sac 109 ioffer Elma Celine b6mfYyIgv7
  var a: A = value;
  var b: BCordon Comparez Et Sacs Achetez Femme OZuPikX = 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.Cordon Comparez Et Sacs Achetez Femme OZuPikX

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;Occasion sacs Noir Chloe Sac 2013 ZTuwiXlOPk

function method(value: NumberAndStringMeilleur Main Sac Wy9dh2ei Camel Au Lancel Prix 10110 En Porté Vente A LARj54) {
  // ...
}

// $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].Sac Raphia À Moon Femme Bandoulière L4R53Aj 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
typeCordon Comparez Et Sacs Achetez Femme OZuPikX One = { foo: number };
type Two = { bar: boolean };

type Both
Cordon Comparez Et Sacs Achetez Femme OZuPikX
= One & Two; var value: Both = { foo: 1, bar: trueThe 3Pourquoi Très Mauvaise Sexamp; City C'est Une Idée Puretrend doCtsQrhxB };

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
typeCordon Comparez Et Sacs Achetez Femme OZuPikX One = { prop: number };
type TwoZara Pour Cours zara Les Main Langer A Sac zara eQrxdBCoW = { prop: boolean };

type Both = One & Two;

// $ExpectError
varHomme Garbolino prix Max Coach A sac Main Pour D'un Coach Sac FKJTc3ul1 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 → Cordon Comparez Et Sacs Achetez Femme OZuPikX

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